The Silent Giant

"The Noctua NH-P1 can handle loads lower than 100 Watts rather well. The temperatures will be high, but modern processors should happily operate at temperatures up to 50°C above ambient – assuming that the internal temperature of the PC case is relatively close to that of a typical household room (~22°C). Prolonged loads greater than 120-140 Watts will have the temperature delta widening too far for the NH-P1 to keep a chip from thermally throttling. The good news is that modern CPUs are designed to handle just such a thing (see: virtually any compact laptop in the last decade), but our testing equipment is another story: we had to stop our testing after 200W in order to avoid damaging our equipment.

We should point out again that these results require excessively prolonged testing time than normal, as the thermal inertia of the NH-P1 is outworldish. For typical PCs, where the CPU is not constantly running at full load, the thermal performance of the NH-P1 is bound to seem much better. Still, we would not recommend using it on infamously hot processors and/or on an overclocked processor. Think something closer to AMD & Intel's standard 65W parts, rather than their extreme K/X parts."

Source: AnandTech