Wow, great stuff so far, thanks to everyone who has already posted. Here's a few things that may help further the discussion.

First my typical cold weather sleeping arrangements (as per a previous cold weather camping discussion here) :

Clothing - a clean and dry change (at least the first night any way lol) consisting of synthetic undies (nylon or polyester usually), a heavy polyester or poly-cotton blend under pants and long sleeve under shirt (i know, cotton bad, but it's a blend, I only use them for sleeping and will have another 100% poly set for day-time activities), wool socks (loose fitting to promote good circulation to my feet), fleece pants, heavy fleece top, toboggan, and fleece tube hoodie (i gather it up around the neck area to help seal up the mummy bag).

Sleeping bag(s) - I use a fleece liner with my current coleman 0 to 20 degree bag (this bag is wayyyyy too bulky for the backpack) ... inside the fleece liner i use these, one or two at my feet and one or two around my core depending on the temperature.

Sleeping pad - nothing fancy, just a simple closed cell foam pad, plus a heatsheet silver side up

this set up helped us sleep warm and cozy on our last cold weather camp out as noted in the thread linked to above.

Now, for the backpacking, I will be using this hammock so I am also looking into the possibility of an under blanket/quilt for the colder weather. I'd really like an over-sized light-weight tarp to help enclose the hammock and protect it from wind and weather but the budget won't allow it for the January camp out. I may end up using a tent for the colder weather January camp out as lows are predicted in the 30s as of now. However, I'm still looking at the under-quilt as an option for future camp outs.

For the sleeping bag, I am definitely wanting synthetic (I am just not very well-versed in taking care of down), a mummy bag style (DS and I are both getting more and more used to it thanks to our current mummy bags).

Standard disclaimers, I have no affiliations with any companies or products I have linked to in this thread.