These cartridges are peas in the same pod...assuming that you handload for the .280. That is key, as much/most of the factory .280 ammo has been loaded to lower pressures than the 7mm Rem Mag. That's enough for me to side w/ the 7mm Rem Mag.
That's exactly why I have and love the 7x57, and don't have a .280 any longer (the 7x57 is a handload-only cartridge, and I like the rifle, character, pinache, etc. I'd much rather tote it around than a .280). For more power, I leave the 7mms for .300s or .338.
