If you do look at quilts, search all the reviews on Tim Marshall from enlightened equipment. They're ALL good. He makes a quality product and his pricing on the Revelation X can't be beat. His quilts have a lot of features, too. A 20*F revelation x will be around 20 ounces, depending on sizing options. Mine which has 30% overfill is just under 24 ounces.
I've got a Montbell #3, and I plan on switching completely to the quilt. It's quality.
I'll be gone the next few days so if I don't reply thats why, but you'll find plenty of info on those quilts in the forums.
Again, I know you're asking about bags, so apologies for suggesting a quilt. But they are worth a look at least. Good luck!