[Assassin]

In gaming there seems to be almost no noticeable difference (except in price) going from an i5-2500k to an i7-2600k or i7-2700k.
You can find reliable and in depth reviews on Sandy Bridge here, and Ivy Bridge here. Note, both link to specific game title benchmarks in a an extended review. Look around on the other pages, and especially the final conclusion for more relevant information.
I'd heartily recommend the Core i5-2500k or Core i5 3570k for any gamer with a budget.
Just curious, Assassion, but why do you recommend Sandy Bridge over Ivy Bridge? Is it pricing or overclocking?
Ivy Bridge (3xxx series) processors cost a little extra, but give the user access to both HD Graphics 4000 (not necessarily relevant for gamers), and PCI Express 3.0--if you plan to buy one of those sexy, sexy video cards.

Also of interest:
Best Gaming CPUs For The Money: July 2012
Best Graphics Cards For The Money: July 2012

You could say both I have been using i5 Sandy Bridge and personally I think its the best and its not like there are features that Ivy Bridge provides and Sandy Bridge does not.