Pentium 641 at -170°C reaches 8320Mhz
 

After mounting it on a Gigabyte P35-DQ6, pouring liquid nitrogen in the CPU pot, reaching as low as -170C, and upping the voltage to 1.95V, they managed to push the processor to a whopping 8320MHz. They would've continued even further if they hadn't run out of liquid nitrogen.

http://www.nordichardware.com/news,6678.html

Done on a P35-DQ6 :) It offers up to 2.35 Vcore without mods, so they have plenty of headroom left once they find more LN2... :-p