In a game’s graphics pipeline it (very generally) bottlenecks around resolution for the GPU and geometry for the CPU. MSFS is pretty heavy in terms of geometry, which makes it hard to scale up with VR.
The best optimizations without improvements to the efficiency of the geometry in MSFS is to use things that the GPU can do better, such as upscaling techniques - so a 80% render that taxes the CPU less (less geometry etc) scaled up via NIS, FSR, DLSS etc helps. If you haven’t already check out OpenXR Toolkit (upscaling, world scale, hand tracking...) - Release thread