Rendering scale, volumetric clouds, ambient occlusion and building LOD are the biggest FPS eater from my personal testing, in that particular order.
Switching to 120 Hz mode also help increase and stabilize fps significantly with my setup but this may be dependent on your hardware strength.
With my 9900K/3090 setup, I could maintain constant 60 fps in non congested areas with small planes using reduced rendering scale, etc. You can tune your settings and see the results in real-time using fpsVR. The main idea is to adjust the settings so that CPU frametime is minimized with little to no fluctuation, then let the GPU carry the load—assuming you have a fairly good GPU. For some reason, this only works consistently for me in 120 Hz mode. This may change as we get newer updates from NVIDIA, SteamVR, as well as MS.