I typically use a 308 for Elk, deer, pronghorn. Makes life a lot simpler I think to pick one caliber and stick with it. I don't take shots over 300 yards at animals so I never really seen the need for a magnum. But I have seen people shooting at geese that are flying higher than 300 yards....
Shot placement/distance is a big thing and you need to think of if you could pass on a less than acceptable shot or would take it anyway.