3.0 cpu overclock

Depends on the quality of your motherboard and the luck of the draw on your chip, but anywhere from 3.6 to over 4 GHz. Cooling will always be a problem for these chips when overclocking, particularly if you start upping the core voltage.
 
So far, I've got my scotty almost to 4Ghz on air cooling. Rock solid and stable. So I would venture to say, depending on what MB you have, will depend on how high you can go. Of course other factors are involved too. RAM, Cooling, etc.