For what it’s worth, I’m having pretty good performance (in my estimation) on my system with a Valve Index headset; under SU4 I was mostly following the configuration settings in CptLucky8’s thread on tuning the RTX 2070 Super for the Index. I’ve got a Ryzen 3700X and a 2070S.
Under SU5 performance has definitely improved (though to fix other things I ended up mostly reinstalling MSFS twice) and I’ve upped a bunch of settings from ‘medium’ to ‘high’ levels.
I don’t know if there’s anything different about the VR runtime for the Quest 2 that would make it worse on a faster system like yours (3900X and 3070).