Ah, so it all becomes clear. The reason Intel introduced part-numbers for their CPUs rather than marketing them on clockspeed is that they're ditching
the high clock-speed Pentium 4 core for future desktops in favour of a lower clocked but higher IPC (instructions per clock) core based on the Pentium-M (which is an incremental improvement of the old Pentium III, which is itself a direct ancestor of the Pentium Pro from 1996).
Though apparently the Pentium-M does have a fair amount of Pentium 4 technology in it, such as improved branch prediction (sort of important when you've a 30 stage pipeline, but helps regardless).
Also interesting to see Intel are going multi-core on the server platform too.