I've got my Q6600 G0 @ 3.8 GHz (1.5625v Bios, 1.5v Everest) benching Cinebench. It's hitting 62c, so I'm sure its not prime stable, but it's on air with my U-120-X. I'm not comfortable juicing it with 1.5v, so I'm leaving it there.

It's running 3.6 GHz (1.45V Bios, 1.39 Everest) Prime stable as my 24/7 clock.