I went with 2oz overstuff on my 0* incubator and I'm really pleased with how it lofts. Overstuff can also help stop loosing heat through the quilt if its windy/draughty.
My 20* burrow has a snap footbox because I like to sleep with one leg bent and thought that being able to unsnap a couple might help with coverage. I haven't tried a sewn footbox to compare, but the snap option works well.
I went with 2oz overstuff on the burrow too. It's a great quilt.