don't have a 6.5/06 AI but I shoot a 6.5 Gibbs, its like this the 280 AI starts with a bit more velocity but check the BC's in the 140 gr weight, the .284 runs just under .5, the 6.5 averages just over .6.
I use a 270 win case, I run .264 berger 140's at 3340 fps from a 29.5" barrel, its an awesome caliber!
whats that about nosler brass not holding primers??
Nosler brass is okay until you use a high pressure load. The primer pockets then loosen to a point they don't hold a primer. If you use loads within spec they do fine. Just don't go nuts trying to push the limits of the caliber.