Assuming the Q9300 does have a multiplier of 7.5x, it would take a mammoth 480FSB to get it stable at 3.6Ghz (the usual benchmark for the Q6600). However, the fact remains that the Q9300 is 45nm and so is very sensitive to voltage, and secondly usually retails at the price of the Q6700. Considering most of the Q9300's are topping out at around 3Ghz or so, it is generally not considered a wise investment. The Q9450 however is said to be the sweet spot of the lot.
One thing to remember is that the 45nm quad cores run a lot cooler and also have SSE4 so if those things appeal to you, I don't see why you wouldn't like them. As for the direct comparison between the Q9300 and the Q6600, at the current price the Q6600 is much better.