For practical purposes, there is no difference. Any .30-06 load under about 3000 ft-lbs in a 24" barrel can be duplicated in a .308 case within SAAMI max pressure. That includes all the loads offered by Winchester, Remington and Federal for example.
Now theoretically it IS possible to squeeze a tiny bit more juice than that out of the .30-06, but the fact of the matter is that the cartridge achieved its hunting and military reputation firing loads that can easily be duplicated in .308.
