Thats bull.. lets take the tbred xp1700 as an example... If you overclock it to the same speed as a xp2400, it will be exactly as hot as the orginal tbred xp2400 unless you fiddle with the voltage.
What? That doesn't make sense. Underclock a CPU then sell it more cheaply? Now
that's bull.
CPUs are tested using certain temperatures and clockspeeds during the development phase. They use statistic analysis to get the chip as fast as possible while keeping the error within defined perameters (i.e. pretty damn close to 0%). The CPU companies want the chip as fast as possible to sell as many as possible, so why would they sell it off at a low speed when it was possible to get more clocks for no performance loss? Answer is, they don't.
Boy, you overclockers are strange. Learn about the manufacturing and quality assurance of CPUs and you'll see what a stupid and unnecessary thing it is to overclock, and to invalidate a perfectly good warranty.