I don'te really think I need a new PSU as my current graphics card uses 8 and 6 pins connectors with around 300 watts at most. 2070S is out of the budget, 470€ top budget. Also, the 2070 is on sale from 520 and on userbenchmark it gets slightly better marks + is cheaper to me. I could get an used gigabyte windforce 2070 super, keyword being used, altthough from pccomponentes.com which is a reliable site here
Don't focus CUDA core count or frequency. Just look at reviews of the 2060 Super, there should be plenty out there and most of them will likely include results for a 2070 to compare. There is typically little performance difference between specific models for a given GPU, e.g. a Gigabyte RTX 2060 Super 8GB OC will perform about the same as any other 2060 Super.