The North Faces Denali ($165; thenorthface.com) is one of the more formidable fleece jackets out there. Its made with heavy 300-weight Polartec, has reinforced shoulders, and comes with elastic cuffs and a drawstring waist to help keep warmth in. And The North Faces Mountain Light ($299) is a classic heavy-duty hardshell, made with Gore-Tex Pro Shell fabric. Throw in some wool underwear (Icebreaker midweight Original Zip, $90; icebreaker.com) and you have a pretty formidable cold-weather combination. Youll want a similar layering system for your legs.
The North Face Nuptse Jacket
But, as you well know, Mount Washington has some of the worst weather on the planet. You can expect wind chill well below zero, and the chance of extreme winds. So, yeah, I think you need a down parka. A pretty heavy one. Check out Marmots Parbat MemBrain Jacket ($325; marmot.com), which has down insulation and Marmots temperature-sensitive shell material that allows more breathability when youre working hard. You seem to like North Face stuff, so the Nuptse from that company ($199) would work as well. For a premium piece, get the Feathered Friends Frontpoint with eVent shell material ($424; featheredfriends.com). That will offer unmatched warmth, breathability, and weather protection.
Id size it to go over the Denali, certainly. That should mean its also big enough to be used as an over-layer in case you need to layer up in a hurry and dont want to take the time to strip off the Mountain Light. Lots of hikers/climbers take that route.
Good luck! Check the weather forecast carefully before you go.