Ok so in my quest to get back to 90 Hz rather than 60 Hz, and knowing I did not want to lower graphics settings in the game, I set a custom resolution in Steam VR for IL-2. I set it to 84% which gives me 2056x2008 in each eye. Still respectable.
Loaded up my next PWCG Spit Mk IX campaign in Bodenplatte. Low altitude patrol - 5k ft - clouds light and scattered.
This may be the winner for me. I was able to maintain 90 FPS the vast bulk of the time, about the only time I saw it drop into reprojection briefly was when I was on runway taking off - right after takeoff it went up to 90 fps and stayed there for the most part. And really the image still looked sharp and great to me, obviously this lower res is still quite above the res of my Rift S. And this running 2x MSAA which I much prefer over FXAA. Had some great combat in this mission, where I downed 5 ea FW 190 A-8's. And the image still looks fantastic, in fact not sure I can even perceive the difference in the lower resolution.
90 Hz just feels so much better to me than 60 Hz. So think I am just going to stick around this resolution and fly at 90 Hz.
Nice to know with these high resolution headsets one can reduce resolution a little depending on system and still get great performance with nice graphics. Then as technology continues to improve grow back into the higher resolutions.