As the speed of the processor increases so does the heat that it generates which. in turn, requires a cooling system that will keep the processor within its temperature envelope. Allowing the processor to work at its maximum potential while keeping the internals cool is the goal of every HSF manufacture. A stock HSF can barely maintain rated temperatures at stock settings, let alone any form of overclocking, especially if it involves an increase in voltage. Upping the voltage increases heat more than raising the multiplier or raising the front side bus. Aftermarket coolers do a considerably better job of taming that fire breathing dragon that hides in your case.



Link: Hightech Hardware