andrewstorm, a little history: When the .308 was first put on the market, the factory data showed a pressure of 55,000 psi. Factory data on the '06 was generally about 49,000 psi--due to the gazillions of old rifles in existence. It was not until the factory introduction of a 110-grain loading in the '06 that a pressure of 53,000 to 55,000 psi was shown.
In the early years, with 22" barrels and 150-grain bullets, there was zilch for practical difference in performance between the two cartridges.