That's the strange thing... I can't. Although, the previous owner was able to run it at 4.0 GHz with 1.25V, granted, he was using vapo. When I received it, it actually required more voltage to run at 3.66 GHz, so I RMA'd the CPU and got a new one last week. This one tends to overclock better with less voltage and runs a bit cooler. By the way, how in the world did you get a C1 stepping?! It's not even on Intel's Processor Specs Sheet. The only C1 stepping they have listed on their site is the QX9770(or is it 5? The LGA775 one lol)