While both the 30-06 & 308 are similar, consider this, the -06 has slightly more case capacity, the 308 has various factory ammo offerings up to 175gr. loads, where as the -06 factory loads have offerings up to 220gr, ( I have considered the fact that past 180gr. it's rare to find 200 & 220gr. loads on the store shelves for the 30-06, but occasionally you do), also depending on bullet weight one would see at the least a 200fps average gain in velocity in the 30-06 over the 308. Accuracy from both is similar, however due to the 308 producing less recoil with comparable loads versus the -06 it would presumably have an edge there. Most guides I have interacted with, when it comes to big game, such as bear, elk, moose and such, have all recommended the 30-06 as a minimum cartridge they would recommend. My personal preference is the 30-06, as much as I love my 270.