For me personally, there seems to be no GPU even remotely powerful enough.
To make my O+ look even vaguely tolerable ( even though it is way better than my VPro ), I have to use HMD 2.0 and SS 2.0 and SteamVR SS at >200%. From a resolution standpoint the multiple upsampling is almost enough to make the text rendering tolerable to my weak eyes. However, despite a 2.1GHz 1080Ti, it's, obviously, a total slideshow. an RTX Titan OC on it's best day is only ~40% faster i.e. a fast slide show with those settings ( by my totally subjective assessment ), i.e. still useless.
That said, I like wickfuts idea of getting the Reverb, with it's much higher resolution and therefore being able to turn the SS settings down so there is less VRAM use and less upsampling-downsampling compute. Kinda counter-intuitive possibly but since we're probably a year or two away from the 'STX 3080 Ti' - I'll take my chances.