Just out of curiosity, have you tried lowering the V's across the board?

I've had mine since the end of December and it's been my experience that higher voltages seem to cause more instability... IDK if it's current leakage or crosstalk or what but that's what I've been seeing with my chip..

As an example, when I was first playing with the HT clock I set the CPU VDDC to 1.3, took it up to 242ht (unstable), bumped vddc to 1.35 and it would freeze at Windows boot screen. So, I lowered vddc to 1.26 and dropped all other v's (expect Mem vddq) 1 bump down in bios, and managed to inch everything up to where it is now.... Which seems stable!

I've been around long enough to know that no 2 chips act the same, but it might be worth a shot for ya...