OCC has published a new review on the ASUS P5Q Premium

Overclocking the ASUS P5 Premium was a breeze. For starters, all I did was adjust the CPU VCore and the memory voltage and lower the memory strap to keep under the 1000MHz memory speed and started to up the Front Side Bus little by little until the system would become unstable or not boot. With each 5Mhz raise of the FSB I would run MEMTEST 2.0 until errors started to appear. Then I backed it down to where there were no errors and booted into Windows. I then ran benchmarks to test stability and again would drop the FSB by 5MHz increments until I could boot, run and pass all of the benchmarks with no errors. With a 1.45v VCore I was able to push the Q9450 CPU to 460MHz from the stock 2.66GHz to obtain 3.680GHz stable. That is a 1000MHz increase over stock just by raising only the VCore and tweaking the minor voltages. While everyone will never get the same results on various systems, I am very please with this boost in "free" performance.

ASUS P5Q Premium Review