While I personally would choose a 30-06 for what you are doing, I think at this point, you are likely to take such a loss on the custom rifle you just bought that I'd just keep it. Maybe load some mild loads for it if you don't want that much recoil. I just don't see that the 300 Winchester Magnum has a huge downside other than recoil. Sure it's overkill, but since you already have it, I'd rather use it than take a big loss on it just to have a slightly slower caliber.