>>273762968
The headsets are all standardized on steamvr at least, and there's revive which let's steamvr headsets play Oculus api games. The controllers are mostly standardized except for the old Vive wands. You'll occasionally run into control issues with old stuff, but you can rebind controls yourself nowdays.

As far as your GPU is concerned, most VR games are running at 1440x3200 at 80+fps. So more than 1080p at 60fps. Some rendering engines don't support efficient stereo rendering so you do get double the drawcalls. 2x is a decent simplification.

Headsets effect performance primarily by resolution and refresh rate, just like a monitor. The old rift CV1 also usedna fair amount of cpu for tracking, but you can't get that anymore. Index has the highest resolution and refresh rate, so it'll require more gpu than rift S or quest link. 

Resolution isn't that different between the modern headsets, so no games will be unreadable on lower res headsets, they'll just look a bit less sharp. None of the existing headsets will render text as well as a 1080p monitor 30cm from your face anyway though. We need about 2x the angular pixel density for that.