Na, it's not too much gun. 300WM is good caribou medicine, but any of the calibers you mentioned would work fine. Caribou are typically the size of a large bodied whitetail or mule deer and some subspecies are evenlarger, but they're pretty slightly built. What I mean is their bone structure is like a marathon runner. They're not built for strength they're built for long endurance. Your average whitetail deer probably has more bone structure than even a large bull caribou. That said your 300 won't be overkill. That's what I use for them just because it's my personal, all-around Alaska caliber. I wouldn't hesitate to hunt them with a .243 and one of my hunting partners regularly does just that. Good luck on your hunt, and get one of those giant bez tined Quebec bulls.

AK Jeff