Can the 260 rem get >3k ft/sec with <40 grains powder, 120 gr projectiles? I don't think so.
The 47mm case can.
Case efficiency is why I give it a nose over.
All other aspects are generally the same.
AI cases never interested me, in terms of fire forming.
I have two 6,5x284's and one 6,5x47L, love them.
The 260 might use a few more grains of powder, big deal. It can still launch any weight bullet faster than the 47L would.
If you want to go off efficiency alone then the Creedmoor's the ticket.
All other aspects 'generally' the same . . . except the x47L can't throw heavier projectiles nearly as well as the 260 if all things are pushed equally hard.
You don't like AI cases, maybe the OP does or maybe even prefers it?
There's a difference between posting facts and opinions stated as facts.
Wayne