Re: 6.5X284 or 280AI
Low recoil, high sectional density for deep penatration, low wind drift values. Despite what many think, this caliber can be used in a short action very well with an extended box. VERY accurate.
Relatively short bbl life. IMHO this can be overcome by NOT shooting matches and letting 1-2 minutes pass before another shot is taken for up to 3 shots in a string.
280 or 280 AI benefits:
More retained energy and even less windage then the 6.5x284. Better bbl life. Also very accurate.
more recoil. Must be used on a long action.
Pick your poison. For deer and antelope, the 6.5x284 gets my vote. For VERY large mature mulies and elk, the 280 gets my vote.
Long range shooting is a process that ends with a result. Once you start to focus on the result (where the shot goes, how big the group is, 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.