yes the 570 is much faster, roughly 30% faster. but your talking about a used card with miles on it. not sure how far hes tried to overclock it or run it at dangerously high overclocks. the 570 came with 1.25gb or 2.5gb of vram while your 7790 comes in 1gb or 2gb. also the 570 consumes much more power and without knowing what your system specs are, more precisely what model power supply, its hard to tell.