Re: scope choice
I shoot the fullsize paper deer targets with a 2.5 - 10x40 buchnell 4200, and a 4.5-14x40VXIII, at up to 700 yards (getting 3 - 4.5 inch groups so I am in the process of getting out further). I say that 10x is not enough if the elk is standing with a backround of similar color. 10x will defintely get you on the elk, but reading the elevation will be tougher if the belly line is poorly visible.
I can understand the weight issue as I live in the middle of the rockies, and mostly hunt high elevation. But if you are going to scrimp on weight I would try and find the few ounce difference in my other gear to get the Nightforce 3.5-15x50.