Troy, I think a couple people might be suggesting the same thing you wrote in your OP, though differed with your self:
You said you thought a double layer of 3.7oz might take your UQ to 20F, but that you thought a single layer of 5oz would be good for a 20F quilt. Doesn't jive.
Personal experience, 5oz isn't gonna hit 20F at all. Maybe 7.2oz, I dunno. Also note other Climashield options under "insulation" at OWF.