I found the key to stability at an FSB of over 475 was gained by tweaking the GTL refs. For example, when I found a sweet combination of fsb tem voltage and gtl ref it was prime stable, but if I changed both of them so that the same end value (vtt*gtl) was being used then the system wouldn't be stable. I don't understand enough to explain why this is so, but it did take ages to find a decent combination of vtt and gtl ref. Also, adjusing my clock skew seemed to help. I'm struggling to get stable at anything above 480 but Brolloks over on ocforums is stable at 490 (x48 board). I can get it to post at 499 but anything over 500 is proving less easy. Probably something needs to be tweaked!

I'm at the edge of what I consider safe voltage (~1.4v vcore and vtt) though so I don't have a lot of headroom to feed it more. Can't afford to kill this q9650! Not yet anyway.