For most games, at this time, single core speed (not necessarily ghz) is the most important thing. That is, a single core CPU that ran 1.5x calcs per second would be better than a dual core that ran each individual core at 1.0 calcs per second. That single core would also be better for most games than a quad core with each core at 1.0 calcs per second.
However, having said that, future games (and even a few current games) can benefit from multiple cores. I would expect this trend to increase.
Depending on the type of games you are playing, it is probably far more likely that your GPU will give out before your CPU.
A final consideration is multitasking, multiple cores allow you to run some other apps/utilities while you game with less impact on your overall game performance.
There are a ton of google hits on this, so its a popular question; but there is no single answer.
Unless you do *heavy* multitasking, and price is roughly comparable, I'd go with the faster speed/fewer cores chip.
On the other hand, if you routinely fire up VMWare to run a virtual machine which you then use to RDP into your work box, while also compiling code in local programming environment, with bit torrent downloading multi GB images in the background and occasionally checking the score on the game you are watching in slingbox player, grab the Q6600.