This is what happens when marketing decisions drive engineering. Engineering is about balancing tradeoffs and Intel threw everything out the window to get higher clock speeds with the P4 architecture. It allowed them to win the mhz war but the performance doesn't justify the power consumption. And the P4 is just terrible with tasks like code compilation.

The Pentium M folded a modern memory bus, SSE2 and other improvements into the P3 architecture with excellent results. From an engineering perspective, it appears to be the better development path.

Ironically, Intel is now going to use product names instead of clock speeds to delineate the products in the new Pentium M line.