Hi @Danger1980Dan and welcome to the forum.
Few months ago I faced the same dilemma: what performance to expect when replacing a 2080ti with a 4090?
This is what I did:
- I set a test scenario with the settings I would like to run and observed that I was GPU bound.
- Then I started to decrease the OpenXR render settings slider up to the point when I observed that I was no longer bound by GPU.
- I took note of the FPS.
The hypothesis is that the new 4090 will do the GPU related work with ease and you will eventually get bound by CPU. That also determines your new FPS. If your 4090 still has some power left, you can use it to supersample for higher visual clarity.
I got my 4090 and the hypothesis above was proven to be just right. I have a G2 and was able to supersample to such a degree that the experience is now like day and night.
For details, if you want, check this post of mine:
With the actual results once 4090 installed here:
Good luck!