WMR HP Reverb G2 set at 90Hz LG monitor with max 75Hz RX 6800 XT Rfactor 2 limits VR frame rate to the setting in graphic options for monitor (options are 50, 60 and 75). Vsync on or off in app and GPU, HMD mirror on or off, SteamVR or Opencomposite. OenXRtoolkit, afterburner and Ctrl+F show the same frame rate. Other games run fine at 90fps (AMS, ACC, AC)
The fix for me with the frame rate in VR is limited to the monitor frame rate is either switch HMD mirror off or switch V-Sync off in Nvidia Settings for rFactor 2.