A few days ago I watch my friend's (known as Lucky_n00b in overclocker's world) extreme overclocking experiments, Clarkdale Core i5 661 (default clock 3.3 Ghz) with Liquid Nitrogen.. On his experiment, he was using this test bed:
CPU : Intel Core i5 661 ‘Clarkdale’, batch# L39B608
Motherboard : MSI Big Bang Fuzion
Memory : A-Data XPG DDR3-1866+ v2.0 ,1×2GB single channel
Graphics Card : GeForce 6200 256MB PCI
Hard Disk : WD Velociraptor 300GB
Power Supply : Antec TP Quattro 1200W OC Edition
Operating System : Windows 7 Ultimate 32-bit
CPU Cooling : K|ngp|n F1 EE Nickel Edition LN2 Container
Others : CoolerMaster Test Bench v1.0



At that time, he managed to reach 6.6 GHz clock speed..


Unfortunately, because he still not satisfied with the result, he does not show me his benchmark scores with his i5 661 at that clock speed. I think overclockers are not easily satisfied with what he accomplished when it really has not reached the limit...

Note: The photo above is taken from Lucky_n00b's workplace's website, of course with prior approval..