One of the things that I discovered when I built my system was that, with my E6600, at a vcore of 1.25 volts (1.35 volts is stock), I could run at 3.0 GHz with stability. Lower vcore = less heat, so the stock HSF should be more than adequate.
At a moderate over-clock - in my case, 3.3 - 3.4 GHz, for price vs. performance; I think that it's hard to beat the Arctic Cooling AC Pro. I cannot, however, reach 3.6 GHz without raising vcore to ridiculous levels (above 1.55 volts).
A quick glance at the specs show that the E6600 has a voltage range of 1.187V-1.325V. Does that mean it's stable throughout that entire range? So I could run it at 1.187V and it should be stable? Or is that the WORKING range, and 1.187V would result in a slower than 2.4GHz clock speed? Basically, if I were not concerned with overclocking, what's the lowest voltage I could supply to it without sacrificing the 2.4GHz performance.