Clock speed is not a god measure of processor speed (rather like how horsepower is not the best measure of car speed, as you need to take weight and wind resistance into account). If you look at Centrino based laptops then they run in the same sort of clock speed ballpark, yet are as fast as laptops with 2-3Ghz PM processors. It's all about instructions per clock, which is tied into things like pipeline depth. Read some of the CPU articles on Ars Technica to learn more.