Re: 6.5 Creedmoor or 300 win mag
Unless you are planning on getting out beyond 800yds or so in the near future, I'd find a 308 in a Savage or Remington and be done with it. Cheaper on the wallet, easier on the shoulder (at least in comparison with the 300WM) and should be able to do everything you need within the distance you indicated you have to shoot. Then, in a year or two, you can move into an AI or custom rifle and start reaching out to extended ranges with a larger caliber after you have had some trigger time on a budget rifle built around the 308.
Also, I'm not sure what your experience with centerfire rifles has been, but if you are just getting into shooting longer ranges, starting with a belted magnum like the 300WM may not be the best option for you (again, going back to the benefits of the 308).