It will depend entirely on the chip you have, as with most things in overclocking.
Some Q6600s need 1.5/6v for 3.6ghz, some require no more than stock 1.35v. Likewise with the dual core. It could require the top end of what ever 45nm chips are capable of, or it could only require a very small amount.
Generalise as much as you want, but unless your buying a tested chip it could go either way.