When I got my .260 barrel, I basically looked at what various factory ammo makers used for their test barrels to publish velocity/energy of their loads and got that. It turns out, for non-magnums, that's usually 24". In the end, I'm actually glad I did that because the Encore platform (I have a Pro Hunter, too) doesn't have an action so it's automatically a few inches shorter than other rifles. Even with a 24" barrel, my PH is (and seems) pretty short and is easily usable in a tree-stand or ground blind (all five deer I got with it this past season were in one or the other, four were from a tree stand, one from a ground blind). I did get a heavy barrel for the primary purpose of adding weight (reduce recoil even more, even though the .260 is fairly mild already). Even with that barrel on it, it's still very light compared to my various bolt action rifles.
I've already been thinking about getting a .35 Whelen (it and the 338-06 are based off the .30-06 brass) barrel for it and have decided I'd get it a 24" heavy or bull (for added weight), most likely a bull.