Bill, hello looks like you've been busy with upper body gear. How 'bout a mithril vest? I heard they are really light :)
I'm getting ready to make a silk/climashield quilt. I've measured my ARC Specialist/X quilt (down) and it measures much wider than your finished dimensions, 54" at the widest area (chest). The other dims are similar, but all around a couple inches more.
I'm trying to get as much info before I make a sample. I'm hoping you can give me some detail on how your quilt covers you. Does it wrap around enough to block drafts when near its lower temp limit?
I notice with my quilt if the edges are not tucked under me at least 3", I feel a cold spot/draft when pushing the quilt to its limit.
I'm much smaller than you at 5' 7", 155lbs. I have wide shoulders though, with a 48" girth.
I sleep with a nightlight torso pad which is placed inside my bivy and then myself and quilt go on top of that. When it gets cold I wrap the quilt around me and use the straps to cocoon myself in. The pad is still under me but not in the quilt wrap. This is the cold weather mode demonstrated on the Nunatak website. I have found this is true in practice providing the best air trap, draft control and thus warmth.
I used some tape on my quilt to get it down to your dims and it really did not seem to wrap around and under enough. I know this is a personal preference, but a cold draft is a draft it seems.
Maybe you are just letting it drap over you and not tucking it under?
Thanks for help, Jhaura