OK, so here's an update on the quilt performance. I added a line of stitching parallel to the sides, on the upper half of the quilt. This stabilizes the down and keeps the center section lofted fully.
I slept out on a night in the low 20's with a little snowfall (remember this is with a bag I designed for 40 degree summer nights!). I slept on a cot, under a tarp, WITH a trash bag as a vapor barrier liner VBL inside the quilt. I wore similar clothing layers to what I would have when backpacking.
SUCCESS~ sort of. I didn't die, but I won't be calling this a 20 degree bag any time soon. By 6 am, I was awake, and ready to come inside. :) in the woods, I would have been the guy who gets up and makes a fire.
I now have confidence in the limits of the quilt as a sleeping bag. I designed it for 40 degree comfort, and I would extend that down 10 degrees with the use of a VBL (ie, my handy trashbag).