Re: 243 ai VS 260 ai
I have both, and of the two the 260 is the one that gets the most use.
you can run 140 bergers a little ove 3000fps. The added bonus is the 260 can routinely smack 1200 yd gong with some authority.
As for barrel life I don't know, I would bet the larger caliber is easier on barrels.
I have about 800 rounds in the 260 and it's shooting groups routinely in the .3s at 200 yds. Really cant ask for much more.