Also worth checking out is what scale they are made at, I remember some of the core i processors were only being made at the higher nanometers scale (e.g. older less heat efficient technology).

It would be ironic if the Core i5 four core model was more battery efficient and produced less heat than the core i5 two core models...

Edit: no, I'm not referring to the recent thing with the sandy bridge architecture, but a previous architecture. Did some more research and it sounds like back in September some of them were produced at 32 nanometers and others were produced at 45 nanometers. Also there may have been some initial problems going to their new 32nm process.

Presumably by now they've got the issues that I remembered sorted out (so that they can have new and different issues like sandy bridge ports and so forth).