For gaming they will be nearly the same. I5 has a slight edge, but you give up the option for those 8 cores.
If you plan on doing multitasking and highly threaded apps then go with the 8 core.
if you only are gaming, go with 3570k.
EDIT: I mean you also could wait for the Haswell processors to come out, which will be better than ivy bridge
Another bonus to having the FX processor, is that the AM3+ socket isnt dead. You will be able to upgrade to steamroller next year when it comes out.
Both have their perks, and both are great.
thank you is there any processors that are better then the intel for gaming