remember there are a hekuva lot of variables. A .308 is an extremely versatile cartridge. However this may not have the kind of knockdown power you are looking for, especially a long-range shot at a big bull elk. A .270 is just a necked-down .30-06. It's a fast flat-shooting cartridge. I personally would go with a .30-06 just for a little more knockdown power. It looks similar to a .308 on paper, but the long range performance will be better with the .30-06. Hope this helps.
Psalm 42:1 "As the deer pants for the water brooks, So my soul pants for Thee O God."