The Magnum shoots the same bullet faster, but not all that much. The truth lays in looking at the ballistic tables and using a bit of common sense at the same time.
The Magnum will outrun the 280 by about 100 FPS or maybe a bit more or less depending on barrel lengths and the individual rifles being tested, but 100 FPS is a good guide line.
So look at the top speed of the 7MM Mag and see at what range it has bled off velocity to equal the 280s muzzle velocity. In most cases that range is going to be about 65 to 70 yards. So in other words, bullet for bullet, the 7MM Mag out-runs the 280 by 70 yards. My 2 questions are:
What animal at what range is going to be able to tell a difference? And what "ambush" can a hunter set up to be 100% sure the 70 yards are just too far to shoot with the 280 but it's just fine with the belted mag? Is it logical to believe you can control the range of all shots in all hunts?
I doubt any logical answers can be made to those questions that wouuld give any real-world credit to the Magnum over the 280. So that's why I say, in the game fields, they are basically the same.
I have owned a 280, two 7MM Rem Mags and one 7MM Weatherby and shot both and killed game with all 3. Given the same bullets ---- there is NO effective difference at all.
