Overclocking To 4 GHz
Of course we had to check whether the Pentium D offers overclocking potential. The answer is a definite 'yes, it does' - but beware of the heat issues this causes! At 4 GHz we had to apply massive cooling in order to keep the system stable enough for benchmarking. Practically speaking, 3.8 and 4.0 GHz won't be doable without liquid cooling.
It is in this area that we see the one place where the Pentium Extreme Edition shines: it is the only Intel processor that comes with higher multipliers unlocked (x14 and above). Once again, Intel seems to be following the path that AMD blazed with the unlocked Athlon 64 FX.
3.4 GHz is a 6% overclocking, which did not cause any problems at all.
3.8 GHz was the maximum clock speed for ordinary air cooling.
The Pentium Extreme Edition ran at 4 GHz, but we can't say it was stable.