I5 2500k is gaming chip of choice, easily clocked to 4.5, is most impressive cpu i've ever owned.
If your doing video editing etc, things that will use hyperthreading, then go 2600k.
But for pure gaming i5 2500k all the way, huge performance.
I would have to say that the Intel® Core™ i5-2500K is the best gaming processor on the market right now. There are few processors that can give you the performance that you get from the Intel Core i5-2500K and none of them are anywhere close to the price.