Rendering with the MAGIX AVC/AAC MP4 - INTERNET HD 1080P 29.97  (with no GPU), it completed in 46 seconds. On the Windows performance monitor I saw what I expected, mid-90 percent CPU usage, little GPU usage, very low SSD and HDD usage. It hadn't let me set a bit rate, it was using the MainConcept AVC encode mode, and the bit rate came out to 3.0Mbit. Playing it back, it looks very nice.

Rendering with the MAGIX AVC/AAC MP4 - INTERNET HD 1080P 29.97 NVIDIA NVENC @ 12Mbit/sec with GPU, it completed in 19 seconds. On the performance monitor I did not see what I expected: CPU usage in the mid 40s (40 - 50 percent), and GPU in the low 20% range. I'd set the variable rate to 12M - 24M, it came out 11.3M bitrate (per Mediainfo).

What I don't understand is why in the GPU render, one or the other of the resources isn't near 100%.

GPU encoders are good at benchmarking NLE's because the software no longer is limited by it's encoding speed (In case of NVENC) The slowness is with rendering(creating) the actual frames, and the NVENC can encode at hundreds of fps at 1080p so it's not the limiting factor

What you see is an inefficiency in the vegas rendering engine. It's only capable of rendering at that speed, and has no use for your remaining 55% cpu 80% GPU. Your gpu can only process at the rate it is sent the frames both for processing and encoding. What could explain this? Latency can, if the cpu is doing nothing for much of the time. You can see what I mean when you use voukoder. It removes some of the latency, your encoding is faster, and your cpu and gpu use goes up.

So you would want to decrease latency. Setting gpu preview to 0 increases latency by a small amount, so if possible keep that at default. Not sure if there's much you can do. Could be an inefficiency at using all those threads. Are they being used equally when you check task manager with GPU encoding?

The limiters are partial what you tell here,using probably FHD and render to FHD.
If you should use heavy 4K sources and render to 4 K AVC or HEVC maybe you see the difference in performance, but you did not tell us that.

Your gpu can only process at the rate it is sent the frames both for processing and encoding.

I was planning to ask an unrelated question, and found your comment!

Is this why Plug-ins that use more cpu or gpu resource than a PC can provide, will sometimes render successfully to tiff image?

Extending on this: Would a tiff sequence saved to tiff sequence have more time/resources for some plugins?

Extending further: Would a video with divided fps also benefit from more time/resources for some plugins?

I ask after finding video saved to tiff sequence with plug-ins that normally fail due to PC specs.

Hope this makes sense.

Thank you for the information. I have tried a busy 4K clip, rendering to 4k as suggested, and the performance is similar. I noticed both the CPU and GPU loading had sawtooth profiles - perhaps the bottom of the sawtooth on the loading graph shows waiting for the other hardware. This would imply that the passing of data from the GPU to the CPU and the back from CPU to GPU is taking a lot of time. My motherboard is a ASUS TUF GAMING X570-PLUS (WIFI), the box says PCIe 4.0 ready.

Rendering with the MAGIX AVC/AAC MP4 - INTERNET HD 1080P 29.97 NVIDIA NVENC @ 12Mbit/sec with GPU, it completed in 19 seconds. On the performance monitor I did not see what I expected: CPU usage in the mid 40s (40 - 50 percent), and GPU in the low 20% range. I'd set the variable rate to 12M - 24M, it came out 11.3M bitrate (per Mediainfo).

It is possible that you are not looking to the right place.
In your case the limiting factor could be GPU Encoder that is not displayed by default in W10 Performance monitor.

If you are checking "Video Processing", it only shows some load used by VP's internal processing.

If you checking 'GPU Activity' (on the left), the W10 is averaging GPU load somehow. It might show you as load is not high enough while GPU parts that is in use (HW Encoder for example) are actually 100% loaded.

For some footage bottleneck could be in GPU Decoder or CPU (if the video stream cannot be decoded using GPU decoder).

Data transfer is usually not limiting factor.

^What he said. There are 2 components to your GPU that do the processing here. One is using the GPU's compute cores... the main muscle they have, to help render the frames on the timeline. From there, there's a special chip on your GPU that does nothing but encode video, so the compute part of the GPU helps finish rendering the frame, then once the CPU and GPU have a frame, they pass it on to the encoder chip to finish processing. It may not require 100% of your GPU power to render the frame (there may only be so many effects used that can even be GPU accelerated), but once the frame is finished rendering, and is sent over to the encoder chip, it then runs at full capacity.

However, I can't say I agree with the above statement about using voukoder, as it too must wait for the frame to be rendered before it is able to do anything with it, so any performance gains there would simply be more efficient use of the encoder chip (or the latency holding VEGAS back from rendering frames faster actually happens after the frame is rendered, somehow).