Yes, this pack is made almost entirely of spectra. Yes, it only weighs 3lbs. 2oz. Yes, it costs a lot of money. Yes, it is extraordinarily well-designed. But does it work on big mountains?
I asked a lot of people that question before I bought one to use on a trip up Denali, and got a lot of different answers. The bottom line is yes, it works for expedition use, with a few important caveats.
The biggest one is that there is only a foam pad for a framesheet, so if you have a twitchy back go with something like a Gregory Denali Pro. Sure it weighs five more pounds, but it carries much more comfortably under heavy loads.
What is a heavy load? Over fifty pounds pack-weight. Pack it carefully and make sure it's adjusted correctly; there's less margin for error with this pack.
As for capacity, as long as you take a "light is right" approach to packing there's sufficient room, assuming you make liberal use of the external tie-downs of which there are aplenty.