As of right now a lot of games are not taking advantage of 4 cores and even less that will use Hyperthreading. But I have heard that upcoming titles over the next few years will utilize more Physical cores as well as Hyperthreading. I play Battlefield 3 and it will use all 4 cores on my i5 3570k. So BF3 and BF4 will even use 6 cores if you have them. If you afford it get the i7 4770k. but the 4670k will run anything just fine.
Get the i5. In comparison, the i5 will do just as good as the i7 in games, since games wont utilize the extra 4 threads that the i7 has. The i7 is meant for multi tasking and business work, that's what the hyperthreading was enabled for, for superior multi tasking ability. They're actually the same thing, it's just that i5 doesn't have hyperthreading and the i7 does.