Some head-scratching differences among the listed specs lead me to believe they're not measured using the same methods. In short, I'd take the compressed volumes with a grain of salt because it could be as simple as that is the volume of the supplied stuff sack. One is not 2x the volume of the other.

Coincidentally, the last bag I bought is from Mountain Hardware, which came with a compression stuff sack, so what volume value do you derive from that?

I don't believe that BA bag is a quilt--it's not stated as such--but it does have a mattress capture system, which is a nice feature I think. It's also far roomier if that is a consideration--the MH bag looks very snug. Efficient so long as you don't move a lot during the night.

Cheers,