I Have the same problem... I have a Gigabyte P55-UD5 + Core i5 661 and the OC is very bad.

I got 150 BCLK rock solid with stock QPI/VTT, vcore below defaut (1.165 vs 1.175), but cannot post if the BCLK is above 150 mhz.

I have the latest BIOS on Gigabyte site, F6

Exists any beta BIOS?