My sleep system consisted of the following:
-20 down bag
2x 57" CCF pads (one Ridgerest, one generic blue foamer)
Stephenson VBL clothes
I was also in a tent and used my GG Vapor Trail under my feet. I could supplement the system with any of my clothes - Montbell Thermawrap pants and TNF Nupste jacket. Everything was a system that worked together, both while the gear was in use and when it was packed on my back.
Like Skurka, I took what I had. I thought about using a two bag system (also have a 30 degree down bag), but I trust the -20 down bag to its rated temp and I didn't want to get an overquilt with little time to test the system.
I anticipated temps colder than what you have stated. I expected lows around -30 and highs in the mid 20s. The record low in Grand Marais for the first two weeks of January is -35, and it is colder up on the ridges. Given the weather over the last two weeks, my estimates were on spot. (On another note, my mother called me last Thursday when northern Minnesota was registering temps in the -30s to state that she was happy that I was at home and not hiking).
In the initial thoughts on the trip, I thought about going with a a wp/b bivy with a head hoop - I eventually purchased an OR Alpine Bivy, but later returned it in favor of a shelter I could sit up in - an Integral Designs MK1. Because it snowed 8"-16" the the first night, I was glad that I was in a tent - I could sit up, move around, keep snow out of the shelter easier, etc. If (and when) I do it again, I think I would seriously look at a bivy and floorless shelter setup. My current thoughts is MLD Superlight bivy and DuoMid for a shelter system.
Are you using an overhead shelter? I know you have a DuoMid, and when I initially read this thread I read that into your stated system. Can your bags fully loft inside the bivy with you in it? It is a bummer that you need wider pads - you should be able to get an appropriate pad at http://www.mcmaster.com/ - you can customize length, width and thickness.
My full gear and reviews is here: http://crazyrunnerguy.blogspot.com/2009/01/gear-reviews-from-sht.html
Randy also has a PM.