The main advantage I see in the .260 is cartridge length, which is short enough to work well in a Model 7 Remington size action, permitting a very short, light rifle to be built for it. Of course, the same holds true for the 7mm/08 and .243 as well. One can also built a .257 Roberts on such an action, but bullets have to be seated very deeply for such a short magazine. The .264" (6.5mm) bore is pretty close to optimum for game no bigger than large mule deer, but the 7mm is also great! Either of these is a little bit more effective for all-around use than the .243.

Keep yore powder dry!!