What settings did you use to get into windows at 500 FSB? If you can fill out a template we can go from there and see what it can do.

Depends a bit on how much you want to thrash it, and how it responds, some Quads will not do 500 FSB but I have not got any experience with them - some guys here do though, hopefully they can give you some advice. It will probably take 1.3 - 1.4 vFSB, 1.55 - 1.60 vPLL and 1.37 - 1.45 vcore, but you should be able to get a little more out of it without pushing it that hard.