For gaming the four cores is all you'll need for awhile. Only a few new games are even starting to try and use 4 cores. Between the two for games, I'd definitely go for the I5 2500k. The 2600k is better for more cpu intensive tasks but depending on your budget it's not worth the extra $100 for games. Unless you are going to use multithreaded applications like rendering, encoding, and photo editing programs 2500k is better price/performance wise.