I would lean towards the 280AI. Brass is available now and it has a proven target / hunting reputation, as in super accurate round.
The 7 max requires a magnum bolt face. If the OP is looking to build on a standard action (which I assume to be the situation due to the original mention of chambering) this would increase his costs to open up the bolt face or acquire a new bolt. Not impossible or even close to it, but something the OP would need to consider.I'd recommend the Sherman 7 MAX.
ADG headstamped brass, fully formed,
Reamers, Dies available. Also custom loaded ammo.
("Son, you know she's a Wildcat".... "I know Dad.. ain't she cool")