Ss 2.0 corresponds to SteamVR 200% and is equal to 4 times the res. Again 2080 Ti will only give you 30% more fps compared to 1080 Ti - it may easily be eaten up by ss. Yes, 2080 Ti is just 30% faster than 1080 Ti, and maybe fun with some res and numbers:
Bear in mind a 2080ti is a 30% performance improvement over a 1080ti.