Not neccessarily true in the case of the P4. It throttles down when the chip gets too hot. However, this does not occur until you reach somewhere around 60ish degrees from what I've read. Some have claimed 55 while some documents on Intel's website suggests 77C. But if you're below 55 degrees, there should be no difference in performance. Everything's regulated by the clock.
"We are Microsoft, resistance is futile." - Bill Gates, 2015.