I have Starline brass for my 308 and have loaded up about 400 pieces of 223 with it. Only the 308 has actually been fired, once. It loaded easily, reloaded without hiccups, and the ammunition shot well.
That's not much to go on; but for me, it's enough.
The CM's sharper shoulder and longer neck has theoretical advantage for bore life, but it's not such a big issue unless one drives the poor beasts hard enough to burn throats. The 260 has more case capacity, and therefore should either A) go faster, or B) go the same speed with less mayhem in the engine room. I shoot the 260 in a longer (28") barrel and do not feel any need to hot rod the chambering. In any case, they both work well, and I made my choice over 15 years ago, when there actually wasn't a choice; except maybe the 260 vs the 6.5x55, which is also a pretty good choice, but not so much for a short action.
Greg