Its for Alaska - but should be able to be scaled down for your windy cold mountain top
ie for my climate region 5B 2" should bring my cold face spot to the outside of the sheathing.
Rather than the 6" for up there in the arctic circle
http://cchrc.org/docs/best_practices/REMOTE_Manual.pdf
http://www.greenbuildingadvisor.com/video-how-install-rigid-foam-insulation-outside-house
http://www.greenbuildingadvisor.com/video-superinsulating-home-rigid-foam
http://www.insulfoam.com/images/stories/docs/JLC-finalfeature.pdf