The Montbell Frost Line parka is a great, warm layer that may be suitable for a Denali climb, but it's going to depend on the season and your other layering options. This is definitely on the lighter side for Denali climbs and if it's your first foray into high altitude cold weather mountaineering, I'd recommend investing the money into a more suitable jacket. I generally recommend Denali W. Buttress climbers have an outer parka with 225+ grams of 650+ fill down. This parka has 190 grams of 800 fill down, so it should come close to the same warmth, albeit a bit on the lighter side. I've seen many guides walk to the summit in their Patagonia DAS parka, but they've mastered their layering system and know how their body performs at altitude and in cold. If you've got a 80-100 gram synthetic mid-weight puffy for lower altitudes, you could always combine the Frost Line and that layer to beef up your layering system and increase your warmth on summit day. If you're planning on climbing in May the temps are significantly colder and you'll want to layer accordingly, but in July summit temps and nighttime lower Kahiltna temps can be as warm as 20-30 degrees Fahrenheit.