As I've noted elsewhere on these forums, when combined with an adequate GPU, Vegas 18 thrives on CPU core speed vs. more cores... According to a Techgage CPU/GPU combo benchmark, the 8-core 5800X actually does better than the 12-core 5900X in their V18 benchmark... So, IMO, you will not see a big real-world difference between your already decent 5800X and the 5900X... However, other apps DO take advantage of more cores and future releases of Vegas may eventually get there. But in this case, AMD's 5950X would more future-proof than the 5900X because it is still clocked pretty fast for a 16-core CPU...

In my case, to handle my paid workflow, I like having TWO or more best bang/buck systems vs. one elite system that can end-up costing 2X more than a single system of mine, but only perform 10-15% better in real-world scenarios. Getting TWO for the price of the single elite system can double my workflow. Using a fast 10g network, I keep a copy of the source video on the 2nd system. Then, when I am finished with the final VEG for that client, I copy it to the other system & have it render-out all of the file types requested by the client while I start a new project on my main editing rig.

In the last 2 years I updated one older Xeon desktop to a 9900K, ASUS Z390 WS motherboard, VEGA 64 LQ, etc. for $1350 and a second Xeon desktop to an 11700K, ASrock W48 Creator motherboard, VEGA 56, etc. for $800... So for around $2,200 invested over a 2 year period I have a setup that renders everything during the work day where I can monitor & deal with any issues vs. hoping all turned-out alright during overnight renders...

I use Vegas PRO 18 on a computer with Ryzen 7 5800X processor, 32GB RAM and RTX 3070 graphics card. If I upgrade the processor to Ryzen 9 5900X I will have some significant performance gain or because I use the GPU to render I wouldn't have it difference?

That sounds like it might be too little performance increase to be worth it now.
I just ordered an upgrade CPU/mobo, but the gap was wide: From i7-6850K to i7-11700K. Five generations newer, and higher per-core speed. (And 2 more cores, 4 more threads, but as TheRhino noted, per-core speed is important to VEGAS Pro 18).

I am quite happy with my 3900X. There is no rush for me to upgrade to get an incremental bump in performance. If time is money and saving a few minutes here and there, maybe.... but count the cost.

Have you overclocked the CPU you have now? I'd do that first (with proper cooling of course) before spending on an entirely new CPU. This is suppose to be the last AM4 generation. Wait for something with the next series, which will require a new motherboard and DDR5 Ram.

Depends on how complex your editing is, I get peaks in 80's and 90 percents CPU with GPU encoding. When editing and ecoding with GPU decode disabled to stop crashing the CPU use goes up. With 12cores you can bother with higher quality CPU encodes at resolutions you wouldn't with lower powered CPU

Have you overclocked the CPU you have now?

Some past AMDs have been hard to overclock but some are getting their 5800X to 4.7-4.8 ghz all-cores with adequate cooling & some trial & error messing with voltage & other bios settings... In comparison, IMO, Intel CPUs are easy-peasy to overclock... By changing just the voltage & clock settings, my 2 year-old 9900K overclocks stable to 5.0=5.1 ghz stable with a $140 Corsair H150i liquid cooler which has a 360mm radiator. However, at 5 ghz the fans are spinning faster & louder, so I typically keep it at 4.8 ghz which keeps the fans silent even during 100% CPU usage. Combined with a quiet VEGA 64 LQ (liquid cooled) I can do voice-overs right next to that system...

My 2nd workstation has a newer 11700K with a 10 year-old Noctua cooler that was reused from the former Xeon that tower case housed. It runs at 5.0 ghz all-cores without messing with overclock settings, which is good enough until I have more time to tweak it. At 5 ghz, it is running 10 degrees Celsius cooler than my 9900K at 5 ghz, so I have some wiggle-room if I choose to overclock and/or try better cooling...

When editing and decoding with GPU decode disabled to stop crashing the CPU use goes up.

I have been building my own Vegas workstations for 20 years, since Vegas 3.0, and have found my current 9900k and 11700K CPUs with their AMD VEGA GPUs are some of the most stable systems I have ever built. I am running them 24/7 for paid work & Vegas 18 never crashes. During crazy weeks I have been editing on one while batch rendering 5-6 clients' projects at once on the other. It's a HUGE time-saver not having crashes. I don't have to figure-out what files rendered & didn't render.

My old I7 Xeons were also very stable, but I can't say the same for past versions of Vegas... However, I have been VERY happy with V18. When I get stability like this I do everything to prevent Windows from updating & ruining everything. I make backup images of my OS drive & backups of those backups...

For those searching for high stability above all else, you could build a system using the exact components of someone else who has been successful... I've stuck with Asus & ASRock workstation-class motherboards with high success, which are noted by the letters W or WS in their names and typically support Xeon processors & registered memory. (although I have never used registered memory in them...) The 9900K is in a Asus Z390 WS motherboard I found open-box for $200 & the 11700K is in a ASRock W48 Creator board I found on sale at Newegg for $200. Previously I had (3) workstations with Asus P6T6 motherboards, I am still using one for importing media from tape, etc. and it continues to be rock-solid 10 years later...

Have you overclocked the CPU you have now?

Some past AMDs have been hard to overclock but some are getting their 5800X to 4.7-4.8 ghz all-cores with adequate cooling & some trial & error messing with voltage & other bios settings... In comparison, IMO, Intel CPUs are easy-peasy to overclock..........

For those searching for high stability above all else,...........media from tape, etc. and it continues to be rock-solid 10 years later...

@TheRhino , you consistently give some of the best advice on this board. A LOT of problems start and stop with ADEQUATE hardware builds. You make that available as a reproduce-able real world formula. Thank you for taking the time to detail all of that. People, pay attention.

You also show that a flexible, outside the box thinking production M.O. will produce more concrete results/speed increase without breaking the bank and relying too much on the bleeding edge, which you've also shown to be not always delivering the goods, YMMV, of course. But we need more "real world" success stories/formulas.

I love the fact they you put heat issues front and center, too many newbies just seem to not understand that dynamic towards stability or non.

Q: Do feel the water cool is most often worth the extra trouble/money? Some say just better employed air cooling is going to get the job done just as well. I'm frankly agnostic and have zero experience with water cooling.

I don't know if you've brought up RAM stick choices as being critical.....Thoughts? (I'm about ready to build/buy that next machine)

I also use two machines.....I'm a bit pissed that the 365 model only allows ONE instance of Vegas, (as opposed to the two - or is it three- machines allowed on the outright purchase...really shortsighted, IMHO)....but sounds like an older version could be cranking the renders anyway??? Does the 10g network require special cards, or is that more or less standard on modern motherboards? Does one need Cat 6?

I TOTALLY agree on the WS model, I purchased an unused HP Z workstation from a 2nd party on Ebay for a steal...and I find that going with a Workstation really does help, and I also have been building Vegas machines for about 20 years or almost....

Got to agree with @TheRhino that core counts don't seem to be a predominate factor in Vegas performance. I use a 4-core Intel NUC on the road which kicks butt over the 6-core xps15 laptop I also travel with. Both have Intel hd630 igpus, 32 gigs ram, and similar speed cpus. The big difference is I hand picked the ram for the NUC and it has an AMD Vega-M gpu compared to the Nvidia 1050ti in the laptop. My philosophy is to go with the fastest, lowest latency ram you can afford that is listed in the vendor qualified parts list. And then run prime95's for at least 8 hours... which is where the cooling comes into play... if the cooling is inadequate or marginal, prime95 will err-out on the small ffts and you'll have to back off on cpu or ram top speeds.

Btw, I'm really fond of the Noctua cpu air-coolers... I like the fact that you can clip on extra fans if necessary. I have a NH-D15 on my 9900k and added a 3rd fan. Haven't done water cooling myself but the closed-loop gpu liquid coolers are pretty tempting. There's also another option I've toyed with: peltiers. Only problem is that pesky 1st law of thermodynamics... it'll suck down more power and creating more heat in the process... but the cooling effect on the cpu is quite good.

Q: Do feel the water cool is most often worth the extra trouble/money?

Don't mess with those DIY water kits gamers like that require connecting your own tubing, etc... Rather, stick to the sealed, all-in-one liquid cooling solutions like the Corsair H150i that are easy to install, quiet & low maintenance as long as your case has room to mount the radiator. My informal tests indicate that the Corsair H150i keeps the same CPU about 5 degrees C cooler than my 10 year-old Noctua NH-D14 but at very quiet fan settings, so I use that system for voice-overs... @Howard-Vigorita I really like the Noctua, but it is so massive with 3 fans that it is hard to reach memory, cabling, etc. which is not a problem with my Corsair... When on sale, the H150i is only about $50 more than the Noctua, and like the app which gives me control over fan speed, etc.

I don't know if you've brought up RAM stick choices as being critical.....Thoughts? (I'm about ready to build/buy that next machine)

Most apps I use show little real-world differences between the different DDR4 speeds, so you're better-off buying more capacity vs. spending that same money on faster sticks beyond 3000/3200 which are a good bang/buck now... Here's what I have in my 2 newer systems.

G.SKILL Aegis 32GB (2 x 16GB) 288-Pin DDR4 SDRAM DDR4 3200 (PC4 25600) Intel XMP 2.0 Memory Kit Model F4-3200C16D-32GIS ($106 USD)

G.SKILL Ripjaws V Series 32GB (2 x 16GB) 288-Pin DDR4 SDRAM DDR4 3000 (PC4 24000) Desktop Memory Model F4-3000C16D-32GVRB

I also use two machines.....I'm a bit pissed that the 365 model only allows ONE instance of Vegas, (as opposed to the two - or is it three-

My original license allowed installation on 3 computers which matched my workflow needs, but since Magic took-over, they dropped it to 2 even though I am buying "updates" to my original license - so not happy about that. Therefore I got another license of Vegas 15 from the "Humble Bundle" for $30 and I just use V15 on an older system I use primarily for importing from legacy media. Remember, you can always start a project in an older version Vegas and finish it on a newer version, but if you start in a newer release, you cannot go back...

Regarding 10G networking, I initially used $35 Mellanox ConnectX-2 PCIe cards & $20 SFP+ cables to connect my workstations to each other, but eventually added a $240 QNAP QSW-M408-2C 10GbE Managed Switch so I could also connect my QNAP NAS at faster 10G speeds... The Qnap switch allows both types of 10G network cables, so my 9900K & older Xeon have the Mellanox PCIe cards with SFP+ (short) cables & my 11700K & NAS have RG45 connectors with longer CAT 7 cables. If you are getting new cables, especially to run through walls & ceilings, get the fastest available - which is currently CAT 8... CAT 7 is fast, but I get occasional dips in speed transferring from one fast M.2 RAID to another fast M.2 RAID, which CAT 8 should eliminate.

@fred-w Thanks for the compliments! My paid work does not require a lot of creativity so I can't support others who need help with new Vegas features, etc. but I do have a lot of experience with Vegas hardware & try to help when I can.

overclock and/or try better cooling...

When editing and decoding with GPU decode disabled to stop crashing the CPU use goes up.

I have been building my own Vegas workstations for 20 years, since Vegas 3.0, and have found my current 9900k and 11700K CPUs with their AMD VEGA GPUs are some of the most stable systems I have ever built. I am running them 24/7 for paid work & Vegas 18 never crashes. During crazy weeks I have been editing on one while batch rendering 5-6 clients' projects at once on the other. It's a HUGE time-saver not having crashes. I don't have to figure-out what files rendered & didn't render.

@TheRhino If you haven't already can you try this benchmark project that someone linked to in another post

https://www.dropbox.com/sh/qoaym1jgpgo8l05/AABec7Jhg_c3jTDJZNxDXB1Wa?dl=0&preview=Benchmarking.zip

My Vegas won't complete the render, and after it fails, Vegas crashes. I've only tried it twice yesterday, have not tried to fix the problem yet. This is with hardware decoding enabled

If you haven't already can you try this benchmark project that someone linked to in another post

https://www.dropbox.com/sh/qoaym1jgpgo8l05/AABec7Jhg_c3jTDJZNxDXB1Wa?dl=0&preview=Benchmarking.zip

My Vegas won't complete the render, and after it fails, Vegas crashes. I've only tried it twice yesterday, have not tried to fix the problem yet. This is with hardware decoding enabled

That file is from here? https://www.vegascreativesoftware.info/us/forum/benchmarking-results-continued--118503/

The Rhino, myself and many others have already done this benchmark. results

Thanks, I'll see what I can do to complete the project while keeping hardware decode turned on. It is a good test as I know completion should be possible even with AMD cpu and Nvidia GPU

I'll echo @fred-w's compliments on @TheRhino's posts—well-informed and very helpful—thanks! Your recent comment on your 10G networking-builds sound very interesting! It seems modern networking technology (especially physical-layer) is finally there.