Focus your attention on what you KNOW you will hunt, not what you MIGHT hunt someday. And, just a reminder that long-range target shooting is for those who've mastered short-range target shooting first.
Without consideration to the bore, my experience has been that rifle (not pistol) bullets from 100-grains to 150-grains tend to perform best on Deer and Pronghorn, while bullets from 175-grains to 200-grains perform best on Elk, Caribou, and Moose. I don't hunt hogs or bears, so I'm going to leave that one alone. However, If I were to hunt brown bears one day, I'll have something that throws a bullet from 250-grains to 300-grains.
Now, obviously, that leaves you some room. By bore diameter:
A .243 with a 100-grain bullet works well on deer-sized game, but can't throw a heavy enough bullet to really shine as an elk cartridge
A .270 will throw a 130-grain bullet that I've seen work well on deer, and though 150-grain bullets are a little light for elk, I've seen it work, though wouldn't consider it a whole lot better than a .243
A 7mm RM will throw a 140-grain bullet for deer, and a 175-grain bullet for elk. Either of which I've seen to be very effective.
A .30-06 OR a .300 Magnum (Win, Weatherby, H&H, Short-, Ultra-) will all throw a 150 that'll work on deer, although the magnums drive them at such high velocity I don't even consider them when the range is less than 200 yards. They'll all throw everything from 180-grains to 200-grains at elk and work very well at short- and long-range.
Given a bullet of the same BC, the faster you drive it, the farther it's going to go. If you hunt beanfields, you may want to look at a magnum. If you hunt the woods, you're probably going to want to stay away from them.
Rifles are like tools. While you can get by most days around the house with a #2 cross-tip screwdriver (Phillips), there are days when you're going to wish you had a #1 or #3 if you're dealing with small or large jobs. You'd no more want to shoot a .300 magnum at prairie dogs than you'd use a .223 to shoot brown bears. There are two schools of thought though. Pick something in the middle (.30-06 or 7mm RM) and hunt everything with it, accepting its liabilities; or pick something specialized (.243 for deer, .300 for elk) knowing that you're probably going to need a bigger toolbox.