RE: Buying a new rifle.
I agree with everyone else in stating that there is no caliber that will consistently buck the brush. That said the rifle you mentioned (Savage 300 WSM) will do what you are asking. There are enough factory loads available that you will be able to match your ammo to the game you will be hunting. One word of caution. You stated you have been using a 243. The 300 WSM will have considerably more recoil than the 243. You should only increase caliber size to the point at which you can handle the recoil. A 30-06 is the same caliber as the 300 WSM but will have less recoil. I would see if any friends or family members have a 30-06 and at least see if you can borrow it for a range session. Buy a box of Federal Premium HE ammo and see if you can handle the recoil and be accurate with the rifle. If you can I would go for the 300 WSM. If not drop down the a standard 180 gr. loading of the 06. If you can't handle the recoil here look to the 308, 270, or 280. These will certainly be minimum calibers for moose.