I actually have a Kimber 84L in 280AI and it is one of my favorite long range rifles. I typically shoot hand-loaded 140gr TTSX at 3200 fps. The stock design makes it's recoil feel less than my light 308.
Here are a couple of groups when I was working up a load. And yes this brass was standard fire formed 280 Rem brass.
3 round groups
5 Round group