I wouldn't expect a lot more than 480fsb stability with a P5Q-E. It's not the top end of the P5Q series and even they have trouble getting 480+. If you want 500FSB+ I'd try a Gigabyte UD3 series, extreme, or USB3. You could also be nearing your CPU limit so buying a new mobo could be a bit of a waste if it doesn't improve things - it did for me though!