If you want to be able to play 2k (WQHD) with highest possible settings you need at least a RTX2070Super or RTX2080. this will give you 60+fps on 95% games on Ultra/Highest settings. A lot of games will hit over 100fps. But, I know of a few games that did not let me hit 60fps on Ultra/highest settings with a overclocked RTX2080, for example Kingdom Come: Deliverance and Red Dead Redemption 2, AC:Odyssey (had do lower 1 or 2 settings to be consistent over 60fps).
Even so I notice recently Kingdom Come runs much better than a year ago. Its much easier to be consistent in the 70s fps most of the time.
Also, if you plan to play with Raytracing, this also changes....I could only get highest settings 60+fps in Metro Exodus with Raytracing on the lower RT setting. But I don't know if you include raytracing into your highest settings requirement. Technically, its part of highest settings.....
Oh, and since you mentioned Witcher 3, this runs with about 100fps on everything on highest setting in 2k with a RTX2080. But don't forget, this game is from 2015, when the GTX980Ti was the fastest card available...