In quite a few benchmark reviews an i5 2500 is around an equal competitor with the two chips flip/flopping. So that is the level of performance. Check out
this page...Could you 5 box on it (the FX8350). Depends on the game, and whether it favours AMD or intel. This matters because of the differences in architecture. Most game benchmarks show very little in the way of favouritism to AMD.
Could you 5 box WoW on an i5 2500; I'd say you'd be pushing your luck with this intel chip these days, especially with the Legion release (assumptions).
I certainly wouldn't want to bet my money on it.
Personally I find an i7 3770k can quickly become limiting.