Hi Dark79, i have basically the same setup (Q6600 + EP45T-UD3R), and i found i had the same problem, 333x9 would boot fine, up to about 375x9. But then i found that to even boot 400x9 i needed to increase the MCH Reference to 0.80v. You might have to fiddle about with the CPU Reference IF that doesn't help, but i found the default setting of 0.760 was fine up til about 450x8.

Tell me how it goes.