In my never-ending quest to improve performance in VR, I stumbled across something I found intriguing and I’m hoping some of you with new 4090 cards can try this out and report your results here.
System Specs:
Asus ROG Dark Hero Viii Motherboard
AMD Ryzen 5950x SMT off, PBO@5Ghz
32GB PC3600 Mem XMP Enabled
2TB Samsung 9800 PRO NVMe SSD
Gigabyte Gaming OC 4090
HP Reverb G2
Thrustmaster HOTAS and Pedals
ButtKicker Gaming Plus
For settings/testing purposes (and fun) I threw everything at it in MSFS:
ULTRA settings, everything maxed, 350GB rolling cache, Real-time air traffic
OpenXR 100%, TAA 100, TLOD 200, OLOD 150
OpenXR Toolkit Motion Reprojection Enabled (UNLOCKED)
Fixed Foveated Rendering Quality (Wide) Preset
HAM Masking Disabled
Loaded in to FlyTampa Vegas Scenery, weather preset clear skies.
Enable the performance overlay in OpenXR toolkit and watch appCPU and appGPU.
It has seemingly been accepted in the community that the PC settings and what is being rendered to the monitor has no impact and performance and members of the community have said it’s just a mirror of what is being rendered to both eyes in the VR headset. This doesn’t appear to be fully accurate.
I went in to MSFS settings while in VR, switched to the PC profile and dropped everything to it’s lowest settings. This appeared to improve frame rate (easier to see if not locking in MR) and help (not solve) SOME stuttering. One way you can verify that changing settings on the PC side HAS an impact on your VR is to drop the resolution on the PC settings to 640x480 and then turn on nametags while in VR. The nametag resolution is rendered at 640x480 and looks like garbage. (The rest of the scenery and everything else is rendered with the VR settings.)
SO, with this in mind, I enabled DX12, went to PC settings, turned OFF Anti-Aliasing, but ENABLED Frame Generation. While sitting in the settings menu to do this, my AppGPU reported from OpenXR Toolkit was showing a pretty consistent 32,000. As soon as I turned on Frame Generation on the PC settings, hit Apply and Save, the AppGPU immediately went to 27,000. Indicating that the GPU was doing less work. And I haven’t even exited out of the settings menu yet. You can turn the Frame Generation off, and the AppGPU increases. Something is going on! 
This implies that frame generation is being turned on for the main render window (to your monitor) and is giving a performance benefit. If this is the case, this means your GPU IS doing it’s own rendering to your monitor and not just mirroring what is displayed to each eye in VR. I’m curious if any of you with 4090s can try this out and report back. Do you see the same thing i’m seeing? Are you seeing any noticeable performance benefits?