Looking at making a warm-weather quilt (~50F). I've seen lots of How-To's that show how to make one with horizontal baffles, and how to do the stuffing. None of them explains how to determine the amount of down needed. For a 50F quilt they suggest 1.5" baffles, but not how much down (850) is needed. Anyone know how to figure this out, or have a website that explains it?

Also, I've seen Karo baffles mentioned, but no explanation of what they are, how (if) they are better than vertical, or (for that matter) how to make and stuff them.