Coolermaster X6 heatsink/fan has arrived and been installed.
Core voltage raised by +0.075 and a simple multiplier increase has the chip running at 4.5Ghz.
After an 8 hour run with Prime95 every core was still active and temperatures peaked at 64*C.
Overclocks past 4.2Ghz with my chip/mobo combination failed Prime95 testing without the vCore increase.
Now that I've raised the vCore, I will see how far it can go on this new voltage.