the 45nm procs. can't have as much core voltage as the 65nm ones but they disperse less heat, so with proper cooling you might accually get a better oc from a 65nm proc than 45nm, but it just depends on what revision and stuff you get.
Tell that to the OCers with LN2, they'll shove in as much voltage as they want to reach a world record

45nm has shorter distances within the chip, thus is theoretically capable of clocking faster.