So it’s oscillate between GPU and CPU limited according your video. Saying that, testing over London is kind of extreme 
and 30 fps is not that bad over this city. It’s one of the more demanding scenery with LA Airport.
Did you check one of the video over here to fine tune your settings? Let me search it…
Here it is 
By watching this fantastic video, you can improve the FPS in MSFS 2020 a lot!
It’s a long video (45min) but do like me : play at 2x thanks to YT option and keep a finger on the Right arrow, you can skip quickly from section to section, and note through paper and pen how to set your games.
Saying that, you should also lower LOD slider Terrain and Object as they spend resources, an also Vector Meshes. Building at more than Medium just change building in the distance, not quality near you (as seen in the video).
For reference I can’t fly over London in VR with my i7 10700K OC 4,9 all core and RTX 3070 OC +125/+1000 and an Oculus Rift CV1,so far lower resolution than your Q2.
My settings allow me to fly at 45fps nearly everywhere when using steam gauge planes ( C 152, Piaggo, Cri-cri, MB339, F-15 Model C, etc.) but London, no. Other cities like San Fransisco or Rio de Janeiro are more fps friendly and I can keep my 45fps (ASW OFF) easily.
MSFS is the most demanding on resource currently. I can play all my other Fly Sims or Racing Sims or video games in VR at my native 90fps and with supersampling… I Hope they will optimize more as it seems.
Edit : One of my favorite area fps friendly is UT25 Monument Valley. Flying between those enormous Rocks smoothly is really great. I also love to go from Courchevel in France to Geneva airport, great scenery and landscape, great fps even when landing.