You don't have a hunt scheduled for the elk. I'd probably go Creedmore, but the .260AI should not really reduce barrel life much if any. The case capacity of the .260 is almost identical to the Creedmore, and the body taper is not tremendous in the first place, so going to the AI doesn't increase the capacity much. Now, Tubb claims the 6XC has substantially more barrel life than a .243 due to the longer neck and sharper shoulder angle. The difference between a 6.5 Creed and a .260 are almost the same as the 6XC vs the .243. The .260 might lose a little barrel life to the Creedmore due to neck length and shoulder angle, but if so, the .260AI may gain it back due to the shoulder angle that is sharper than either of the others. Whatever the case, the .260AI is not particularly overbore. Personally I'd rather shoot something faster on prairie dogs which brings a second gun into the mix, and I'd rather shoot a 7mm or .30cal on Elk.
It's hard to beat a 6.5 Creedmore.
I know this might sound crazy, but to actually try to fulfill all three roles with one gun, you might consider a .308 or 30-06. You could run 3300-3500fps with 110gr bullets for a flat shooting PD load, 3000fps with 155's for steel and deer, and shoot 215's-230's on elk. Barrel life would be a non-issue. The biggest problem would be throating it for all three bullets, and the answer would be to throats it short for the 110's and seat everything else deep. Loosing that case capacity would suck for a .308, so the 30-06 becomes a better candidate. For each of those roles there is a cartridge that would be quite a bit better, but to span the whole range, the cartridge would actually be adequate.