I've been wanting a .280 rifle for awhile now but I've just never pulled the trigger. I ended up getting a 7mm Rem. Mag. thinking I can load it down to .280 levels if I want to. The plan is to work up a good magnum load, and a good .280 level load for times when I don't need or want the extra velocity and recoil. What will likely happen is I will work up a good hot rod load and leave it at that. I still want a .280 for some reason. The nice thing about wish lists is that they don't have to be rational for anyone other than the person making the list.
.280 A.I. sits right between 7mm-08 and 7 Rem Mag.
7mm-08 162 gr at ~2700 fps MV
.280 A.I. 162 gr at ~2900 fps MV
7 Rem Mag 162 gr at +3050 fps MV (180 gr at +2950 fps MV)
Yes you can load down a 7 Rem Mag to be a .280 A.I. In your case, adding another rifle, I would suggest a 7mm-08 or 7mm-08 A.I. Really knock down the recoil, and it is still a great performer.