Without knowing the respective down 'fill power' (FP) of each option, I don't see how you're really able to compare apples to apples in terms of loft & weight.
Here's some really fundamental math that makes the exercise pretty straightforward:
1. standard 80" x 50" quilt = 4,000 sq inches
2. multiply by 2" loft (ie avg target for 30- degree quilt) to get 8,000 cubic inches. (Btw, 2" is also the baffle height.)
3. divide by 900 FP yields 8.90z of down
4. multiply by 1.35 (ie 35% overstuff) gets you 2.7" of loft (avg target for 20- degree quilt) and another 3.1oz of down, for a total of 12oz of 900 FP down.
So, for around 12oz of 900 FP down, you can get a quilt that has a loft in excess of 2.5" that should be good enough for temps to 20 degrees. If you use M50 (actually, .7 oz per sq yrd coated [9 sq ft] or .078 oz sq ft * 55.5 sq ft [8,000 sq in/144]), then your total fabric weight should be in the range of 4-5oz.
With 12oz of 900 FP down and 5oz of M50 and 1oz of nano-seeum, you can have yourself a nice quilt in the 20-30 degree range that weighs around 18oz. Problem is, about the only way to pull this off is MYOG, and there's only one real supplier who provides a turn-key package, but it's only $170.