I’m still testing, but abandoning the OpenXR toolkit was a mistake. The massive FPS loss in VR is also noticeable after a short time under SteamVR. This also applies to the current MSFS version. The FPS deterioration outside of VR is noticeable, but not as blatant as in 3D. Nevertheless, it is practically unplayable for longer than 15 minutes. This is undependent of MSFS- or 3rd-party-aircraft.