2070S to 3080 user here. Try setting the Visuals up higher. You’ll get the potential clarity without the smoothness but at least you can see what is possible with the 3090 clarity wise 
It’s a difficult one. How can I recommend something that costs almost 3 times the price of a 3080 with only 15% extra performance? You could always order one to try and return if you don’t think it’s worth it. It is a pretty penny for a small visual jump. You can get a very satisfying experience with a lot of games with your 2070S but I completely understand the pull of a new graphics card
Ugh I wasn’t much help 