RAM 32 Go

You are asking for "Which GPU" and my question was which choice you have.
That question you did not answer

What price range are you aiming for?

Also keep in mind, a new gpu isn't a magic bullet to instantly grant you better performance. For instance, the video from my Panasonic S1's is 4k 10 bit 4:2:2. Buying a new GPU will do nothing to help me decode that faster, as no GPU can currently decode that video with hardware. Getting to the bottom of what is causing your bottleneck is important. To do that, we need to know what kind of media you are editing, and what your project settings are.

Hello

Apparently I didn't understand the question.

The videos are in 1080p 24 fps.

But originally either 1080p 60 fps or 4k 360 25 fps.

Sincerely

Gpu hardware processing ability is very format specific. Better if you cut and paste the footage metadata from MediaInfo. Far as I know, Vegas only supports hardware hand-off from mov and mp4 containers. In general, if you can afford them, you want to go with gpus with the most recent decoder chips such as Intel 750/Iris, Nvidia 3000-series, and/or AMD 6000-series. Previous generation Intel 630, Nvidia 1600/2000-series, and AMD's 480 and later are not bad either and more affordable. Generally they're all good choices for encoding and display, the AMD and Nvidias are the best choice for video fx and multi-stream processing, while the Intels are best at decoding.

For the decoding there are no worries.

But some video effects are computationally intensive.

My GPU is new and less than a year old but it seems to be a 2016 model.

I was thinking of AMD RX 6900 XT.

I'm thinking in terms of a 6900xt myself but glitches have been reported by 6000-series users here with the picture-in-picture fx that necessitates a work-around. 5700xt had a similar issue till Vegas developers fixed it in an update. A number of users here have the Nvidia 3080 which seems well supported by Vegas... which I assume would apply to the 3090 too. But if you check out the spreadsheet in the Sample Project Benchmarks thread, a 6800xt tops the list... that benchmark is dominated by the computationally intensive Noise Texture media generator.

@Howard-Vigorita,

I also consider an update of RX6800xt or even just the RX6800 in a future time. In comparising with RTX3080 and/or RTX3070ti at current price factor, the AMD-card has

plus:
best harmony and efficiency with my Ryzen5950x
huge VRAM that benefited by 4kfootage and also by HDR10-editing
overall better timeline performance
overall better acceleration by (HDR10) rendering
-the Nvidia card is excellent in gaming with lightFX etc., but not really strong enough in 4k-editing for my machine (I assume)
-the studio driver aims for stability yet drops its gamingFX away(?) and who knows what else, too

minus:
no 10bit-depth encoding with video convert app (yet I have a powerfull CPU)
driver performance mucks now and then as reported (the new one 21.9.1 seems good)
not a real competitor with Nvidia in most games (though I never play them)

@LuluBent, I think a so called professional graphic card not really making sense in video editing.

-the studio driver aims for stability yet drops its gamingFX away(?) and who knows what else, too

I think stability happens due to delaying rapid release of modifications for latest game releases, if no problems with gaming drivers they get added to studio drivers.So you get everything with Studio but maybe a month later, and the system seems to work, game drivers normally the ones that cause editors problems but not studio

@LuluBent Hi, i can't give you the info others can but my GPU is a GeForce 3090 24GB, i have a 32core CPU & 256gb RAM but i still have to 'Build Dynamic RAM Preview' to get some fx & transitions to play right,

What i do now is Build Dynamic RAM on a large section where i'm editing or the whole project if it's only short, this takes a few minutes but once it's done the project will play correctly, I leave the selection at that area & then if you move/edit something the software only has to update that part when you click Build Dynamic RAM again,

Like on this where i overlayed images on a board, then i swiped my finger like you would a phone screen, the images on the top track had to have a wipe transition but i couldn't get it to play at the correct speed to get the timing right ,

so i selected the whole thing, Built Dynamic RAM Preview, that took a few mins, i left the selection as is in the pic, then after every edit when i moved the pics or transitions i clicked the Built Dynamic RAM, it took seconds to update & be able to play at the correct speed.

Give selective pre-rendering a try as well, they made it way faster in VEGAS 19.

I also consider an update of RX6800xt or even just the RX6800 in a future time. In comparising with RTX3080 and/or RTX3070ti at current price factor, the AMD-card has
.. .minus:

no 10bit-depth encoding with video convert app (yet I have a powerfull CPU) ...

@Yelandkeil I can confirm the lack of vce 10-bit encode up through the 5700xt. Then again in my ffmetrics quality tests, 8-bit vce manages to top Magix hevc Nvidia 10-bit render quality and isn't that far behind 10-bit qsv.

The image within the image is a function I often use. I've never had a problem with it.

In fact I find that some of the effects are less fluid and not slower.

On the other hand, the Warp Flow transition makes Vegas crash.

 

The image within the image is a function I often use. I've never had a problem with it.

In fact I find that some of the effects are less fluid and not slower.

I don't think you mentioned what card you have but it would be GCN architecture not RDNA, it's 5000 and 6000 series cards that have had the problem drivers, not only with Vegas.