The best upscaling methods are called DLSS and FSR (Nvidia technology and AMD respectively). They’re easy to use and with your GPU either method will work, even the AMD technology, although FSR is only available at the moment when using DX12. Give both a try and see which works better for you.
In the options, under the anti-aliasing setting just choose one. After choosing one of them, the next box below it will be which “quality” setting you want to choose. Try the different quality settings and find one that looks good and performs well. It’s that simple. I use FSR and both the “quality” and “balanced” settings look good to me ;).
Regarding all of the other ways to set the render scale like in the PiTool, Nvidia control panel, OpenXR Toolkit etc. just set them all to 100% and only adjust the quality setting for DLSS and/or FSR. Regarding the in-game settings like volumetric clouds, texture resolution etc. just move them to their highest setting and then back them off 1 notch meaning if ultra is the highest for a setting then back it off to high.
The only other setting that has a big impact is the “motion reprojection” setting for VR. I don’t have Pimax so I’m unsure, but I leave MR off.
You should be able to get good results like that. Once you get it working then you can tweak the other settings, and try motion reprojection, but keep it simple to begin with. Good luck.