Where is boxer/big stick when you need him? Ok kidding, but there are lightweight rifles (Rem mountain, ks, tikka light and superlight,etc), and there are really lightweight rifles (NULA/ULA/Forbes, Kimber, weatherby ultralightweight, custom, etc). I've hunted WY for the past 18 years and think I've seen about every possible "mountain rifle" there is. My experience says that a rifle must fit well, and the shooter must be able to shoot it well, or you could spend millions and not gain a thing. If he truly is a new hunter (and assuming a newer shooter) shooting mag calibers out of seriously lightweight rifles will only lead to frustration instead of learning. A reasonable elk caliber (which could be anything from let's say 7-08 upward) on a light but not too light weight rifle would probably serve him much better in the long run. Unless he is doing a serious high altitude sheep/goat hunt, or doing an on foot backcountry wilderness hunt where every ounce matters and is carried on your back, most people can get by with an extra 6 oz to a lb of rifle weight with no trouble at all. My personal "mountain rifle" for the longest time was a weatherby ultralightweight in 30/06. Killed a lot of elk and mulies with that rifle and never wished I had bought a mag or larger cal in that rifle. I currently have quite a few mountain type rifles in various makes and calibers as they lend themselves well to how I hunt. For me, the rifle needs to be an accurate one and one that I can shoot well. If it doesn't meet both of those criteria it gets traded or sold. The biggest thing for me is to pick an appropriate caliber for what you want to hunt, find a rifle that fits well, and learn to shoot it well in field conditions. He will be much better served by doing that than by comparing rifles on paper. Once he gets a handle on what he needs and what he likes, there are a ton of options for true rifle loonies. The tikka suggestion (both light and ultra light) is sound as is the Kimber 84m or L or if he has to have a mag cal 8400. A nice used or new rem mountain rifle and even a model 7 would do as would a win mod 70 fwt on the heavier end.

Good luck with the choice

Craig