I was finally messing with 500FSB other day (posted in MFII thread), it is a hit and a miss, 1 minute ok next minute not ok and very hard to work out what it needs to stabilise it.

That's why I say its the lack of Bios support.

I may look into your MFII bios if I can find it and it aint too old.

I have seen the lower range Asus P45 getting higher than the MFII thats why I assume ita lack of support.