Clock speed is not everything. You need to consider your cache and bus speed as well. It it were a car, it would be like comparing the displacement without looking at the horsepower or torque. While it may be a generally good metric, it doesn't always hold true. An atom processor only has between 512k to 1mb of cache and clocks around 2GHz on the high end. A P4 on the other hand has 1-2 mb of cache and clocks at around 2-3 GHz. If power consumption isn't an issue, the P4 is the obvious winner in my opinion.