I've seen a few places reporting the .243 barrels have issues stringing around a bit with more than a couple rounds. 6.5CM sounds pretty hot OOB, and I havnt heard much on the .308. (Preordered a .308 and will try 6.5 later, though pissed when I found out diff. length handguards).

One guy with a .243 on a forum swapped it out with a custom made 6mm or something and was getting absolutely sick 1/4 MOA out of it. Dont have link handy sorry.