anchor,
Given that the OP is in S Idaho he might be glassing for mule deer over miles, literally. I've hunted the other side of the Snake River and you could spend days glassing the breaks. In fact, there are some groups that set-up in Idaho and glass across the Snake into Oregon. So although different than sheep hunting the opportunity for long distance glassing is still there.
I think Jordan's post is another good example of determining the distance and size of object before settling on a certain objective size. A 50mm isn't the best choice for antlers at 2 miles, at least not the ED50.
J
