i was reading duru3d news when i came across this.

wowA Japanese guy clocked his Pentium 4 670 (3800 MHz) towards a blazing 7133 MHz today. How he did it ? He raised his FSB a teeny weeny bit towards 375 MHz. In combo with a 1.7 Volts CPU voltage, good gear and hey .. some Liquid Nitrogen he was able to maintain the frequency.
I really doubt if the processor and mainboard survived this small project though ..