Here are the settings I’m using to hit 90Hz on the Pimax 8K X in Assetto Corsa. They might still need some tweaking, but they seem pretty good in the bench mark at least. There are some frame drops but I only noticed them because I was staring at FPSVR. Some of the settings are pretty high and could easily be lowered if needed.
PiTool quality 1.0
SteamVR SS 100%