Get the .30-06. Here are my reasons.

If you later get more rifles that may be suited to special purposes, the .30-06 will be a suitable back-up gun for anything you hunt in North America. If you are driving from Texas to Wyoming, for example, to hunt pronghorn antelope it might be a good idea to carry a second rifle in case your first rifle breaks or is otherwise incapacitated. Otherwise you may have wasted money on a tag, a long drive, hotel stays along the drive, and vacation time and not get a chance to actually hunt.

If you foolishly forget your ammunition on the coffee table at home, you should be able to buy .30-06 ammunition ANYWHERE that sells ammunition, maybe even a feed store in Lone Wolf, Wyoming. Will you find the WSM loadings in a feed store in Lone Wolf, Wyoming? Will you find the WSM loadings in a feed store in Lone Wolf, Wyoming in the year 2015??? If the feed store sells centerfire ammunition, I would bet good money they carry .30-06 cartridges.

The .30-06 is good on coyotes, deer, pronghorn, sheep, mountain goats, elk, moose, hogs, and black bear. Most prefer something heavier for Grizzly Bear and Brown Bear, but many Grizzlies and Brown Bears have in fact been taken with the .30-06. Thus, I argue that the .30-06 is suitable for taking any North American game (however if it were me I would obtain something heavier before going on an expensive Grizzly or Brown Bear hunt, the cost of the rifle would be a small fraction of the remaining cost of the hunt anyway).

Most people can shoot the .30-06 without any flinching problem. Some people develop a flinch with heavier cartridges, such as the .300 Winchester Magnum. A rifle you shoot accurately is better than a more powerful rifle which you shoot INaccurately.

Out to 300 yards, there isn't any significant difference in the flatness of the .30-06 versus the other higher velocity cartridges. Most of us, myself included, don't shoot well enough to justify shooting past 300 yards on pronghorn sized game anyway. Most shots are, in fact, at less than 300 yards. When you have advanced in the art of marksmanship to the point where you can hit consistently in the vitals in real-life hunting situations, from field positions at 400 yards, that might be a good time to relegate the .30-06 to a "back-up" role and purchase a real long range rifle, if you find yourself needing the extra distance in the hunting situations that you encounter.

Just my $0.02 . . . or maybe my $0.04.