I had the same board with a Q9550, you should be good for at least 475FSB, very possibly, 500-510FSB, depending on your ram,
I would use Load-line calibration,
and try setting your MCH latch to 333mhz, seemed to give me a little better stability overclocking.
only voltages I had to increase for a successful overclock were,
CPU core voltage
CPU Termination voltage (VTT/FSB)
MCH(north bridge) Voltage
Ram voltage, depending on your ram, since your trying for higher FSB speeds I'm guessing you have PC2-8000 or PC2-8500
Oh I forgot I should also tell you, once your above about a 425Mhz FSB with that board, if you have the PLL voltage set to Auto, it will jump that voltage really high, it only needs to stay at Default voltage, 1.50 I think it was.
On my Q9550 for a stable 3.8Ghz
CPU core, Vcore - needed 1.344 with load line calibration, this was read in CPU-Z in windows. I believe in the BIOS it was actually set to 1.36,
CPU Termination/Vtt - I had around 1.3 I believe, or 1.34
MCH/northbridge voltage - took around 1.3 - 1.34
Make sure you have good case airflow,
make sure you have a good CPU cooler, don't let the CPU temp go over 70C, stress test with Prime95 Small ffts
I would suggest a Antec spot cool fan over the North Bridge heatsink, it can get toasty with the higher FSB speeds and the higher voltage.
Good luck!
