wow, holy hell what a friken mess.
OP, it doesn't make a tiny bit of a difference what cpu you get for gaming. whether you go with a 3.6 ghz dual or quad, or a 4 ghz dual or quad (unlikely unless you get a QX), it doesn't make any difference.
Unless you care about other things, like media encoding or 3D rendering, cause that's all cpus are good for, and soon not even that (cuda). For gaming at 1920x1200, and im sure you will max out AA and AF filters, cpu matters very little.
If you don't believe a person with a 4 ghz QX9650 and a pair of GTX 280s in SLI that has tried all kinds of combinations like disabled cores down clocked cpu to meticulously examine the impact, then by all means go with all the other biblical advice in this thread.
And by the way, add GRID to the list of games that utilize quads. I have seen my cpu peak to 65% usage during game play. And still, with 2 cores disabled I get exactly the same fps.
Hmm.. maybe I would see the difference if I turn down the resolution and lower my settings to medium. Wouldn't that be humorous after you spend 1500 dollars in graphics.