Re: .308 or 300 win mag?
Another ditto, I started with the 308 and still have 2 or 3 laying around and one I use more than any other rifle. Even out to 1K.
The 308 will do fine with the right bullet. Learn its pathe and wind and youre good to go.
Long range shooting is a process that ends with a result. Once you start to focus on the result (how bad your last shot was, how big the group is going to be, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.