I agree with Dirtfarmer on the 6.5-06....
I have had two of them and have not had any problems with forming brass or burning out throats. Forming brass was as simple as running the parent case through the 6.5-06 sizing die and start shooting.
Sounds like you are pretty well set on the 260. If that is the case (no pun intended), I would talk to the gunsmith doing the chambering and go from there. He can tell you what you need to do as far as the magazine, throating, ect, to make things work smoothly. Then let him do it.
One thing I would do for sure, no matter what cartridge you decide to use, is make it with a sporter contour barrel. No flies on turning down that Bartlein 5R down to a sporter contour to fit the Legend stock....
