Water Cooling Is Recommended For 4.0 GHz
3.8 GHz is all well and good, but 4.0 GHz lets you tackle and beat the current Pentium Extreme Edition 965 (even though it's not yet available at retail outlets). To this end, we boosted the FSB clock rate to a full 200 MHz.
Overclocking by 50 percent shows this 2.66 GHz processor booting at slightly over 4 GHz
To keep the system stable at a 50 percent overclocking level, we had to increase the core CPU voltage yet again. We took the same incremental approach described in the preceding section. Finally, when the voltage was increased by 0.2875 V, the system continued to be stable at 4 GHz, even at maximum load!
At 4014 MHz the Pentium D 805 remains absolutely stable and is thus overclocked by about 50 percent.
Although the Pentium D 805 offers only a 1 MB L2 cache, its CPU clock is also 276 MHz faster than the top-of-the-line Pentium EE 965 (equipped with 2 MB L2 cache); this enables the 805 to outperform the pricier chip.
CPU Rightmark also shows a CPU clock rate of 4 GHz.
This is where the Zalman cooler begins to show signs of stress. In fact, its maximum fan rotation speed isn't enough to handle the terrific levels of heat produced; the CPU gets too hot, and begins to throttle back its speed.
The violet line clearly shows that when loaded, the CPU begins to throttle back through the intervention of Thermal Monitor 2. Though this prevents the CPU from burning up, it also slows things down.