Well it depends on whether or not you're really planning to overclock, and if so, how much. The Q9300's 7.5X multi might be harder to hit high overclocks than the Q6700's 10X multi.
However, it it were me and that was my choice I'd pick a E8400. Oh wait, that's not one of the choices.
Just kidding. You could go with the newer tech of the Q9300, 45nm (spelled cooler), and you can still take it past 3Ghz. If you're considering the Q6700 you may want to take a serious look at the Q6600 as it is better price/performance and you can still overclock the sh** out if it, quite easily. The Q9300's 7.5X multi is not an overclocker's dream.
My .02