If I was going to get a 300 mag of any kind I would go right to 200gr bullet's. But something you did not mention I wonder about, bedding. After I get a few shot's with a new rifle out of my system, I go through the bedding. I've found most rifle's can be improved with better bedding.
couple sheet's of typing paper need to go between the barrel and stock and touch no where. Then tighten the action screw's and slowly loosen the front screw watching the barrel in front of the action, no movement at all should be seen there. You can also see it at the front of the barrel channel, even more pronounced! See it, bed it.
