Although I don't own, or shoot a 280, My choice would be the 280 Rem. You will be shelling out some dough, so That would be my choice. I have hunted out here in the West all my life, and my rifle is a 270, w/130grn bullet. A mule deer is a large animal, and will take some punishment, before going down, if you hit where you need to!
![eek :eek:](./images/smilies/eek.gif)
For me anyway, I think the 243 is a marginal cartridge, when it comes animals the size of a "Muley" I will probably take some heat for that statement, but a good friend of mine shot a blacktail with a 243 , at less than 150 yards. The bullet hit the rib cage, and just did a lot of bruising, and skipped off. He had to track that blacktail for most of the day. He killed the deer with his wife's 270, so he didn't have to track the deer anymore! This is the story he told me, and would not doubt him in the least. He is not a "BSer"