I look at the .260 and .280 with essentially the same eyes. Each is a more efficient variation on the parent case, providing better ballistic performance with reduced recoil. Obviously, an AI modification will increase performance, but I am far from convinced that I need the additional performance, additional recoil, or (perhaps) additional throat wear. The part I like about both is that they fall somewhat short of the overbore category, which suits me. My next logical step up from the .260 would be the .280. I would not stand out on the range at 1200yd in front of a .280 with higher BC bullets.
I have a pair of .280's, both Ruger 77 MKI's. One has a sporter barrel and is perfectly suited to deer hunting; the other has a Varmint weight barrel and has been my load development rifle for accuracy. Working the way up from 120gr bullets, I reached the 150gr level, and had to interrupt the project in favor of load development for shorter range rifles. I hanker to return to the project, and should be able to next shooting season. So far, Nosler BT's and H4350/4831SC have proven to be strong allies to the accuracy effort. In comparison to some projects this one has been a bit easier. The more accurate loads in the 150gr weight class have been with 50-55gr of these two propellants.
Greg