I think the Speer manual characterizes the 280 as being a practical equivalent to the 7mm mag, but with less recoil. This is based on the small difference in velocity between the two. I also note that there are some attractively lightweight guns in 280. Personally, I'd go with the 280. But if I didn't handload, I'd use the 7mm mag.
In my case, if the 270 is inadequate for the game sought, then it is most likely that the 270 WSM, 280, 7mm mag, 30-06, and many other 30 caliber guns will be inadequate too. Therefore, get a bigger gun.