After my first post, I went to the Winchester Ballistics chart. With a Winchester Power Point bullet, 150 gr. (I know... bullets are a whole new discussion... but I wanted a constant) I compared the 308 with the 270. The results are close.
Sighted in at 50yds with 1 1/2 inch sight height
270
50 yds line of sight 0" - speed 2717 fps - energy 2456
125 yds line of sight 0" - speed 2524 fps - energy 2120
308
50 yds line of sight 0" - speed 2665 fps - energy 2364
125 yds line of sight -0.1" - speed 2444 fps - energy 1987
The next question is recoil. The stronger the "kick" the harder it is to put the next shot on target. I have no experience to comment on either caliber. Note that a semi-auto will absorb kick.