Generally speaking, the i5 is better for gaming than the i7. The i7's default speed is 100MHz faster than the i5 and it has Hyper Threading (HT) capabilities. Based on a review from Anandtech sometime last year HT does not improve gaming performance based on several popular games. Some games had a 1% or 2% decrease in performance. Therefore, the extra $80 - $90 for an i7 2600k vs. an i5 2500k is better spent on a video card or you can simply save that money.
However, based I saw a link to a video which showed Resident Evil 5 having about a 10% performance increase with HT. But that is just one game.http://www.youtube.com/watch?v=dSfduuG0tIA