I checked out XtremeSystems and a few of the people there already own a Conroe. they posted pics of their step by step OC, and the performance of the E6400 was amazing to say the least. from 2.13Ghz to 3.0 on *stock* voltage.
65nm in itself wouldn't make a very big difference, its the new architecture (K8L) that has any chance of topping Conroe. As it stands, AMD has no hope of any Athlon 64 processor it puts out having any chance against Conroe.