I necked my '06 up to .338-06 and I'm glad I did. Now I want to neck one down and shoot a .280 (possibly a .280 Ackley). I'm on your side in thinking 24" barrel (or 26") for the sake of velocity.

The 6.5 should give you slightly longer throat life than a .25-06, there are tons of cool-kid 6.5 bullets out there... so why not?

I guess I'll play devil's advocate here and ask if you have long range rifles you don't shoot, why not go for a heavier bullet for a medium range / hunting gun? Something like... oh, I don't know... .280 Ackley?