Some of the calibers that really shine on the long range target shooting may not have a lot of thump left for big game at very long range. My personal rule is 2,000 fps impact velocity. Below that, bullets are generally able to make a wound channel only the size of their frontal diameter - which is what muzzleloaders and pistol calibers do. With that in mind, I would opt for the 25-284. But, as others have said, there are a lot of other calibers that can really carry the mail at distances beyond 500 yards if necessary. The .257 STW would be worth looking at . . . .