I'll throw another wrinkle in if you don't mind. I have 6.5 CM and a 7mm-08AI. Got the CM first, then put the 7mm-08AI together. After owning both, most of the advantages in a non factory barrel are imaginary for the 6.5CM for the handloader. You get a factory barrel that is twisted right and some decent factory ammunition w/ the 6.5CM.
If I were putting together a rifle w/ a custom tube and wanted a 6.5, I would do 260AI w/ Lapua brass. You get the twist you want (because you picked it), Lapua brass and the most powder capacity of the standard short action chamberings. Yes, the longer bullets will eat into the case capacity, but more is still more - you will get better performance w/ the 260AI.
I'm running my 7mm-08AI in a Kimber 84m which is really tight in the mag constraints. At no time have I wished I had picked a 7mm CM instead. Brass and bullets favor the 260AI.
YMMV
David
