Hey, the .280 is a great cartridge! I currently own a 24" Rem 700SS. I run 154 Hornady Interlocks right at 3000fps with 59-60grs of H4831 depending on lot. I've run 154s at 3015 with 61grs R-22. Quickload says that velocity with R-22 still under 62Kpsi. Since you're asking, the slower powders give the best velocity with less pressure. R-22, N165 are the best for me.
My basic velocity ceilings for the 280Rem in a 24" bbl is 3150 for 139s/140s, 3025 for 150s/154s, just at 3000 for 160s. With proper powder selection only though.
By the way, I've lurked a while here...nice site.