I have the 2080 XC Ultra from EVGA, and I was doing some reading on watercooling for the different cards. There is definitely an improvement , however I believe it will be marginal. I would say a 5-10% increase in performance, for a 7% increase in price. The 2080 has 2,944 CUDA cores, whereas the 2080 Super has 3,072. The super also has two more Ray Tracing core.
I can't tell you exactly what this means for you. I can imagine you may see some more frames, but you won't be going from 60FPS , to 100 if that is what you are expecting.