I am not a down expert, but ultimately isn't warmth directly correlated to loft, when comparing down head to head? So many other factors at play in terms of shell construction, but if comparing only the down ...
"What we obtain too cheap, we esteem too lightly: it is dearness only that gives every thing its value. Heaven knows how to put a proper price upon its goods; and it would be strange indeed if so celestial an article as freedom should not be highly rated." Thomas Paine
| 
