I don't really see the point of layering down (or synthetics). Down (or synthetic) insulates by allowing the heat from your body to warm up the interstices between filaments. When I sleep in a good down bag, I'm actually colder if I wear something that prevents heat from getting into the bag (e.g. fleece jacket). Instead, I just wear a midweight long underwear layer, hat and good socks, and am really toasty even in very cold temps. It seems as if the heat from your body would hardly reach the second layer of down, so all you end up having is a bulky "shell". You might as well just throw a hardshell over your down jacket to achieve the same result, with far less bulk and cost (I usually use a $50 Marmot Precip).
In my opinion, you want to buy a really good down jacket (or two), but keep the amount of material between you and the down to a minimum. Don't skimp, as poorly made or lower-quality down jackets (and bags) have cold spots, which are huge heat sinks and really decrease the efficiency of the down. Search around, as there are always good deals online. There is never a need to spend MSRP on quality gear.
For the record, I have a MH Ghost jacket and a MH Subzero Parka. I can go out in -20F for a few mile hike (nowhere near as strenuous and bodyheat-generating as a high altitude climb) in the MH Subzero Parka with nothing but a t-shirt underneath and be too warm. I have also used the Subzero on our SAR team's winter survival training and have been very warm and comfortable, even sitting around "camp" for extended periods in high winds and very cold temps.
The lighterweight, hoodless Ghost routinely sits in my pack on climbs with temps around zero, and I very rarely put it on for anything but the descent.
EDIT: While I very much respect Kelly Cordes, most of us will not climb at anywhere near his level. His gear selection is well thought out and tested for his style of alpine climbing, but that may not necessarily apply to most of us chumps (including myself) who are happy to make it up Orizaba, Denali or a bunch of winter fourteeners in our lifetimes...