OCC has published a new review on the Intel Core 2 Quad Q9300

Overclocking each processor is different. With five identical processors you will get five different results. With this Q9300, 456x7.5 was the point at which it was prime95 stable. It would run benchmarks at up to 470x7.5 but was nowhere near stable. Above 456 FSB, the amount of voltage to keep the chip running was significantly more than what other 45nm processors I have tested have taken at similar FSB and raw clock speeds. At 1.55 volts there was no point trying to even push further. The good news is that the CPU would do almost 450 FSB on the stock 1.215 volts. I left the volts at 1.34v during my testing just as a safeguard but have since lowered this to 1.31v at 456 FSB. Pretty low volts for the clock speeds I was able to pull from the little brother of the QX9770. Having a motherboard that will allow high front side bus speeds with a quad core processor is essential with the Q9300 CPU. Raw clock speed is limited because of the low 7.5 clock multiplier. In order to reach 3.6GHz you would need to hit 480FSB, something not all quad core CPUs will do, some, but not all.

Intel Core 2 Quad Q9300 Review