I really like both 4831's the IMR is faster when temps are warm but both are about the same velocity when its cold due to velocity loss with IMR. H4831 is prolly the best all around powder for the 280AI if you get accuracy you like, next up would be RL22.........
I too used R22 in the only 280AI I ever had, with both the 150 and 160. I have been playing with R26, which is supposedly more temp stable. I get outstanding velocity in my 7mm Rem Mag and the 160, and even over 3000fps from a 22" BAR 270 with the 150!