You don't need an i7 for gaming. You should be focusing your funds on the graphics card, as this is what will ultimately hold you back from achieving higher settings and framerates in-game. The unlocked i5 is going to perform just fine for gaming, the only difference to the i7 is that they i7 has hyper-threading and thus four "virtual cores" as well as the four psychical cores. That being said, if your budget is high enough for a top graphics card as well as the i7, knock yourself out ;-)
Scroll down to the "diminishing returns" section here:
http://www.tomshardware.co.uk/best-cpus,review-33354.html