What type of distances will you most likely be shooting at moose/elk? 200 yards max? 400 yards or beyond perhaps? Do you reload? If so, do you reload 30-06 or 308.....and have a healthy supply of bullets to choose from already?
You said that you have many bolt guns already. For a moose or elk hunt, why not pick one that you shoot well with in any of the following cartridges:
30-06 / 270 in a long action, or 308 /7mm08 in a short action.
If this is an excuse to build another rifle in a magnum, then any of the magnum cartridges already mentioned would work for N.A. game.
The weight of a magnum rifle would be the least of my worries if hunting in the mountains out west was the plan.
Hint: Cardio at sea level vs 7000ft above sea level is a tad different. 3 years out from your hunt, so you have some time to prepare for it, along with time to get aquiainted with a new rifle in a new cartridge.