Overclockable further?

[Emission]

I was overclocking the rig in the sig with cold air (comp in the window, its winter here), and I got it to a stable 3.72GHz. Even though I was able to push it to a minimally-stable 3.87GHz, Im really curious if theres any way I can heighten its stability. It can run at 1.6v but everytime I try 1.625v it freezes up, regardless of the conditions. I cant quite figure out if its the cpu limit, or a board limitation or something. Suggestions?