Free: Contests & Raffles.
Your 300 RUM is a great all around rifle. I can't imagine anything it wouldn't do. But I guess you must be looking for something lighter, and perhaps with less recoil? I would go with a 270 Winchester or maybe a 30/06. You really can't beat the 30/06. But if you want a little less recoil then get the 270.
I have both a 270 and 30/06. The 270 recoils less using a 130 grain bullet versus a 150 or 165 in the 30/06. Admittedly, it's not a significant difference. If you can shoot a 270, you can probably shoot a 30/06 just as well. There's no advantage to the 280. It's a great cartridge, I'll give it that. But the 270, 280, and 30/06 are all so close they're virtually the same. What one will do so will the others.The 280 is great if you want to shoot something that is "different" especially if you're a reloader. If you don't reload, there's no sense in paying extra for ammo that doesn't perform any better than the 270 or the 30/06.