Could you give more details on how to do this ?
Sure, so I wrote a TLDR summary post here. I'm certainly not the expert here so I wanted to write up a steplist of what I did for others to test and / or modify for their own use.
Note before you start that the correct values are going to depend on your headset and your headset software's SS options before you get to SteamVR, or Elite's in-game settings (each option is an interacting step in the chain towards the final image you see in your headset), not to mention GPU capability. By default, the higher you set your headset options, Steam Auto will reduce quality to balance the performance on your system. I'm maxing out the headset's SS option and then manually overriding Steam to a fixed 0.25 value. The way PiTool does pixel to pixel mapping may differ from the HTC or Oculus implementation etc. Finally, a small boost to the game's HMD value using 1.25 on top via EDProfiler because my system can handle it.
You'll probably need a bit of time to read from the beginning to get better context!
Here's my steplist (note syntax error in your Steam personal config will cause it to reset to default and you won't see any benefits, and don't edit the standard config, that gets blanked with every Steam update but also clearly tells you not to edit it):
https://community.openmr.ai/t/best-quality-settings-for-steamvr-ive-found/22614/48
Further up, here's an example of Steam telling you your headset's resolution based on your headset SS setting (x2 in PiTool in my case, if I set to x1 then Steam would show a different answer) - note this is 100% NOT your headset's physical resolution so don't use that, it will be wrong. And going from x1 to x2 is, I think, not doubling pixel demand but
quadrupling it due to the mapping method. Which is why Steam is 'quartered' to match.
https://community.openmr.ai/t/best-quality-settings-for-steamvr-ive-found/22614/43
The calculation of the recommended resolution depends on a multiple of the above (in my 5k+ case with a res of 8532x5264, the lowest multiple is 4266. I can get away with 8532 on Normal 150 FOV. On Large 170 to overcome any quality loss with that width, I tried 17,064 which looks gorgeous on the text, but even a 2080 Ti struggles to maintain 30fps in stations on that setting. And that's factoring in the other performance settings utilised (I'm aiming for a solid 45FPS because I effectively get 90 via the Pimax frame 'doubling' option, plus PiTool can use Fixed Foveated Rendering on RTX cards which reduces the quality outside of your field of view).
On wide FOV headset like Pimax (and a little bit on Index but hidden away), the canted lenses need additional transformations to work correctly with Elite called Parallel Projections, and that's a GPU performance hit. So much of the above is to max performance while getting the best possible image quality. The idea is to not to get the most amazing image ever possible, that can be done with silly SS settings, but to get best cleanest image at the best possible usable FPS.
Appreciate this is a fair bit to take in, I'm still learning a lot myself. I hope it's a helpful starter location to understand VR optimisation with all the current options available to us. Any questions let me know, I'll do my best to explain. There are people on here who have far more expertise than me on this!
I am now ultimately waiting on the 8KX with ultra high native res to provide a clean image without the GPU overhead of high SS values. But I'm very happy with what I'm running on the 5k+ now, it's a better balance than anything I had before.