What Rifle Calibers Bring Down the World's Toughest Game Animals?

There are the hard to bring down animals that require a little more firepower than you'd normally use. We're thinking large animals with tough hides and mean dispositions here like the Cape buffalo. Some of the larger animals may even call for extreme rounds like .375 H&H Magnum, .470 Nitro Express, .404 Jeffery, and other large calibers that are as punishing to your shoulder as they are the animal itself.