No, it's not the quads, it's the mobo. Seems it sucks at 45nm Quad FSBs even more than with 65nm Quads. I am still struggling to get FSB 467 (--> 4,2Ghz) fully stable on my Q6600. 456x9 has been stable for days now though, using Bios 0603.
Even though I'll have to upgrade to 07XX as soon as I get my D9GKX mems, thanks again for pointing this out guys.