If most of your shots are going to be within 150yds, you really don't need a 300RUM. It packs quite a bit more punch than the 300WSM. In all reality, you don't need a 300WSM at that range either. Especially if you're just shooting deer. A 30-06 would be plenty. It works just fine on elk all of the way out to 300-400 yards. (Possibly even farther if you're a good enough shot, but I personally wouldn't try it).
But if a 300WSM is what your heart is set on, get it. Otherwise, you may regret your purchase later on.
