I think this decision could be a lot more complex than it needs to be.
The guy is not a hand loader,so he is likely pretty practical and would benefit from a wide variety of commonly available factory ammo so that he can find something that shoots well in his rifle.
I could scour gun emporiums from New England to Casper(have) and further; only the very best stocked will have 280 ammo,and I bet even fewer would have even a box or two of 280AI. Scratch one for the 7 Rem Mag.
If I blindfolded him he couldn't tell the difference in recoil and blast between a 7 Rem Mag and a 280AI in a thousand rounds.The "recoil and blast" of a 7 Rem Mag are mythical dragons in a rifle of reasonable weight. 4-6 gr of powder simply do not make or break a cartridge on that basis.
The 280AI is a cartridge for far gone rifle nuts(SuperT nailed this) obsessed with tiny differences (I get it being a loony myself).
But I can pop into a gun store and "buy" factory 7 Rem Mag ammo whose ballistics are identical to the 280AI;and if I choose to load my own 7 Rem Mag ammo,can easily equal or exceed what a 280 or 280 AI can do.
As an all round, go anywhere BG cartridge in that category, the 7 Rem Mag beats all comers at their own game from the standpoint of ubiquity,ballistics,popularity,and availability....not to mention terminal performance.
Easy choice.
