ANYTHING that you can kill with a .300 RUM, you can also kill with a .30-06. About the only thing the RUM does is extend your range. You just have to get a little closer with the '06.

Alternatively, the RUM has a variety of "power level" ammo, so you can buy factory rounds loaded to .30-06, .300 Win Mag, and .300 RUM power levels, which clearly makes the '06 and RUM redundant.

If it were me, I'd want more separation between calibers. It would be helpful to know more about where/what you plan to hunt. i.e. "Bears" is a pretty broad term. There's a big difference between a 150 lb black bear and brown bears or polar bears.

I don't much care for magnums, and wouldn't use one unless I was hunting for something that might consider me a food item. So, I'd probably go with something like a .243, or a .257 Roberts or a .25-06 for a "smaller" cartridge, and a .308 or .30-06 for bigger stuff, up to and including elk/moose. If I was going to limit myself to a "2 gun" arsenal, I wouldn't choose to .308 caliber cartidges...