How for can push my p4 1.6a with stock cooling?

[zck250]

I've got a p4 1.6a and an msi 645 ultra with pc-2700 ram. How high can i overclock my cpu and not overheat. I want to run around 125 fsb. The only problem is that i cant see my temp, becuse msi's bios read it wrong, it says i'm at 49*c without overclock.