which kind of cooling do you use Emperor ?
If you got good enough cooling, it can be vdroop stopping ya, or bad cpu stepping..
I've got a Pentium 4 Northwood 2, 2.4 GHz (533 fsb) which can't go higher than 3060 mhz using watercooling that can get my C2D up to 4 ghz,
My board is a P4C800-E Deluxe, which vdroops 0.1V.. I've lent it to Nosfer@tu to vmod it, and then I will try again to see of it helps to higher oc, or i'll just have to satisfy with, that i've got a lousy cpu stepping.. heh =)
Edit: is it a Northwood C or a Prescott ? and which stepping, or take a CPU-z screenshot and post it ^^