Actually if you have a 2070S already, adding a 2nd one might not be so bad at all!
Given the lack of 3080 and 3090 and reading your topic, I wanted to find out and here is a video showing some results with a bunch of games:
RTX 3080 (10GB) vs RTX 2070 SUPER SLI (2X8GB) || INTEL i9 10900K || PC GAMES TEST || - YouTube
It looks like in this case:
2070S x2 (SLI) = 3080 x1
Not bad at all given the price and this makes me wanting to try out.