If you mean total system poweruse, then its by far better to integrate the NB onto the CPU compared to having a separate chip as a NB, since no power will be needed to get all the signals across, less logic is needed and CPU's usually get made on a far better process than separate NB chips.
I can see what you're trying to say though, but wouldn't you rather have a chip that gets just a tiny bit hotter, but results in both better performance and lower system power consumption at the same time?
I for one would prefer the latter, even more since that'll mean you can easily customcool that part of the system aswell, resulting in even better potential overclocking.