4ghz limit?

[SharonB]

I have a P4 cedar mill 631 (holding me over for a few more weeks till q9450) and I have been getting pretty brave with it now that I know I'm going to get a new processor, but I seem to have hit a limit of exactly 3.99ghz. Why? I messed with the voltage of the cpu ( all the way to the max Intel said was safe 1.325V). Is it a ram problem maybe or have I just hit the limit of the cpu. It boots all the way to windows at 4.27ghz but instant bsod. I know its not a heat problem ( or I'm pretty sure its not a heat problem) because in the bios it says about 35C. Anything I can do to maybe get the speed above 3.99ghz. It works great at 3.99ghz, no problems at all and it helps so much its not even funny.
I hope the q9450 doesn't have the same problem (I'm sure it wont)

Other info:
FSB: 275-280
Mobo: Asus Maximus Formula
RAM: Gskill 1000mhz ( hope thats not the issue because it was such a good price)