A lot of interesting replies; elevation gain vs. miles is something I never considered....I expect it's a very true statement.
I plan on doing an elk hunt within the next couple years and I'm setting up my rig now. I got a good deal on a Remington 700 KS, 300WM that is 7.06 lbs without the scope; it'll go slightly over 8 lbs when scoped and loaded. I just wanted to make sure I didn't get too heavy.
I'm still young enough (44) and in good enough shape to cover the mileage most of you spoke of, but the weight of a good animal on my back would probably make me question just how fit I am.
I truly appreciate the replies, it's given me more to think about.