KS v9.0.286. Note that I had to update graphics driver to 441.20 to get it to work. The nvidia Optix doesn't work with anything less than driver v435 or so. This is a single machine with Ryzen chip and dual nvidia cards, not two separate machines, so the comparison is 'apples to apples' as the saying goes.
CPU Rendering (Ryzen 2990WX) - 499 fps
GPU Rendering (Dual nVidia RTX 2080Ti) - 403 fps
Looks like the FPS counter has a bug. Check the sample count
1 : 13 - CPU vs GPU
@Eugen are you saying that the actual FPS for the dual 2080Ti benchmark should be 403*13 = 5,239 FPS? Or am I misunderstanding you?
Its been talked about before, but yeah the FPS does't corrolate between CPU and GPU. Dries posted a conversion somewhere, but it is still approximate.
The CPU delivers higher quality per sample, so it is not quite the same as one GPU sample. One way to assess the speed of the GPU vs. the CPU is to render an offline image with 100 samples on the CPU and then render the same image on the GPU with 100 samples - and possibly increasing the number of samples to get the same quality. With the setup and performance you are seeing you should expect the GPUs to be quite a bit faster. I recommend using 9.1 (beta) which has significant improvements to the GPU sampling (higher quality per sample).