Some Questions about Foveated Rendering

I just wanted to ask some questions about VR and Foveated Rendering.
Firstly, what fps do you need to make VR stable and useable, because I have seen many websites saying that no VR setup reaching below 90fps is suitable? Is this actually true or is this just a way for companies like oculus to support various other GPU and CPU producers? I normally use graphics software running real time Ray/Path tracing at around 25-30fps and it feels completely stable, and I do realise that the main fps decreasing factor for VR is having to render two viewpoints simultaneously. Would 25-30fps be useable, obviously not from a gaming POV, but from more of a immersive visual experience? So what I mean is not the kind of VR where you are constantly having to duck turn and jump around shooting things, but instead the kind of graphics visually display based VR experience. So would 30fps be suitable or not?
Secondly, with foveated rendering, can you decrease the fps of the visuals outside of the periphery? Would you be able to render all of the display around the eye at 60-70fps whilst rendering everything else at around 25, or can you only decrease resolution not fps?
What I am mainly trying to achieve is photorealism within VR. I am looking into Omni verse software, and am seeing very high end realism. I put this post in the VR section because the majority of the questions are based around that.
I have access to two high end 3080 PC’s, and my question is, could you use one PC and one 3080 to render each eye instead of splitting rendering load between a single GPU? I am looking for the kind of photorealism shown in the Omni verse Marbles At Night demo. I understand that a 3090 is significantly more powerful than a 3080, however because I have access to two 3080’s, I decided that I could use VR to render the image(s) due to the implementation of eye tracking and foveated rendering. Because foveated rendering roughly decreases resolution to 1/3 of the average, could I get fps stable enough to visualise it in VR properly without breaking immersion or having very bad motion sickness? The Marbles Demo was run at 1440p on a 3090, so could I get it to run at 4k for periphery, then minimum (whilst still accurate for foveated render) for the rest of the display, at around 30fps or higher?
Just a few questions, thx

I may have some thoughts for your first and second query. (First) although there is no standard fps for VR headsets, modern VR are constantly improving the fps because higher frames lead to better immersion. I actually do not remember the paper title, it is from MIT/Stanford, they suggest 1800 Hz is the appropriate refresh rate for VR to match with real-world visualization. In that sense, 90+ fps has become a standard. (second) You cannot have two different frame rate in a single scene (fovea, and periphery) because it will lead you to jittering effect, and the flickering will also increase. Do not forget, due to dense rod distribution, the peripheral vision is more sensitive to motion.