Q8200 has a lower multiplier, so if you planned on overclocking that will play an impact as youll need a higher FSB to reach desired clock speeds than you will with the Q6600's 9x. Stock or OCing, I would still pick the Q6600.
8200 will run cooler, and is the one I'd choose for not overclocking. If you want to overclock though, I'd go with the 6600. You'll probably hit a higher clock with it, as the 8200 would require a really high FSB, and I wouldn't trust an Nvidia board to hit the kind of bus that would be required for a decent overclock.