My observations on the performance of the 280, regardless of bullet selection or weight, is to steer you toward something larger bore. The 280 is a little less of the good things you find in the fast "magnums," but at the cost of a little less recoil.
Going bigger, while I love a 30, i think means going past a 338. I have seen magic happen at 35 caliber. 35 Whelen brass are made from '06, 270, 280, etc. That eliminates the availability problem of half your newly required components. Bullets in 35 are always scarce, now is no exception. But the demand for .358" always seems to get a run of each bullet annually. And you can use .357" jacketed pistol bullets in a pinch.
I realize this a long range forum, but we already left that boat behind discussing a straight 280. If you are wanting to go long range, a fast 7 or 30 is a lot more than the 280. A lot. And you increase effective range a lot over a 280. Especially using soft bullets like some Berger or AMAX/ELDM.
So back to bigger bore, if you're willing to cut some distance for power: 375 h&h was mentioned. It is proven, and you can use the Speer 270 to greater results than the 280, at near the same trajectory. The next most popular big'un as far as ammo seems to be the 45/70. Thats a capable medium/long range round in the right gun, but I am thinking a lever gun with semi-custom ammo like Buffalo Bore or Garrett. If you have killed with 12 ga slugs, you know of what I speak. Otherwise, think of broad, deep wounds in almost all critters, from prairie dogs to moose. I have not killed said moose, but others have documented those results well.
I have killed with flat nosed cast bullets and will again. Kills are decisive and spectacular, though ranges are limited compared to your 280.