Hard to argue with the success of the 7mm Rem Mag.
The .280 is a fantastic round, is what we set my sister up with for big game, and it's served her very well. But it's also not much of a step up over the 6.5 Creed, basically going to give the same trajectories with a little heavier bullet. I would choose the .280 over the 6.5 CM for hunting, but I wouldn't sell a 6.5 CM to buy a .280 for hunting.
I use a .25-06 for elk most of the time.
Have you hunted here? Doesn't sound like it. I've been in a lot of elk camps over the years, seen a lot of different rifles carried. .45-70 has never been among them. You're far more likely to find someone using .243 here than .45-70.