I know I'm gonna jump into the frying pan, but I thought that when the army chose a cartridge, that one of the conditions that needed to be met was to be able to kill a man at 600 meters.
Hence the tried and true .308 and .30/06.
I would use a .223 on deer. I think that too much is put on horsepower, and not accurate bullet placement. A large caliber rifle, and a bad shot may not equal a recovered animal, where an accurate shot with a lower caliber cartridge can yield very satisfying results. JMHO
You can't kill'em sittin' on the couch!