I and some friends of mine used our 6.8s for 3 seasons to kill game and the tally as of right now is 38 deer and antelope killed with them. It's a fact (and not just an opinion) that the 6.8 is good to at least 450 yard on western Mule Deer giving through and through wounds with wound channels about as big around as an egg. Of the3 38 game animals killed by myself and my friends 5 have been over 400 yards (lazed with range finders) and all but one had an exit wound. The one that didn't was hit by a friend at the root of the tail and the bullet was found under the skin at the base of its neck. It was a very large deer. In fact, that was the largest deer of all the deer killed by us. A big Montana Mulie.
Remember guys, the cartridge is relatively new, the its basic ballistic recipe is quite old. It's just a bit better than the original 257 Roberts which is a very good deer round. It fired a 117 grain bullet at 2620 FPS. The 6.8 fires a 110 to 115 at 2650 FPS to about 2775 FPS. So it's going to do just about what your grand dads old 257 has been doing for about 80 years.