I've seen my fair share of caribou killed, as well as a handful of mountain sheep, and I will repeat that any bullet that will reliably kill large deer will work fine on those animals.
My experience with 'bou is that if you hit them in the right spot, they go down with just about any bullet that you can send into their vitals. Hit them wrong, and they are liable to go for miles, regardless of caliber or cartridge used. I've seen them put down with authority with the .25-06, .257WM, .243, .308, etc, etc, and I've also seen them stand there and absorb four 225gr Fed SP's from a .338WM. Some are tougher than others, but if the first shot hits the boiler room, they are going down for the count, pronto. Sheep are just as easy to put down, IME.
