In the field, energy at impact is key to a clean kill. Bullets such as the Berger Hunting product line compensate for decreased energy at long distances by opening up a sizeable amount of flesh. In my opinion and 40+ years of reloading, shooting, hunting deer, antelope, and elk: 25 & 26 caliber OK for deer sized game. Even .264 is light for elk and moose, but if you need a one rifle to do it all, then the 6.5 is the smallest that I'd go for. 270 & 7mm have taken lots of bigger critters, but I'm strictly a 30 caliber guy for the big boys. 270 is a great round for an elk/deer gun with primarily deer in your sights. However, the bullet choices are much more versatile in 7mm and 30 caliber to optimize reach and accuracy while having enough energy to make the clean kill. Being an old man now, my 300 Win Mag is my go to gun for elk and moose. 25-06, 257 Weatherby and 6.5-284 for deer.