The NB is just as important if not more important that the CPU speed. A good example would be the following two links

These are Super Pi 1m runs.

This one is with CPU @ 5000MHz and a NB @ 1000Mhz
http://www.hwbot.org/compare.do?resultId=809287

This next one is with CPU @ 4231MHz and NB @ 3000MHz
http://www.hwbot.org/compare.do?resultId=811581

Which of the above do you think has the higher run....