Well, the Yeti is part of the Warbonnet system, too. And my thought is you'll still be cold in the stouter quilt if you haven't figured out how to stay warm in the Yeti at 20+10 temps. That said, I'm a believer in the Wooki style quilt which does take away a lot of the potential for error. You'll still need to find a better way to deal with wind as that will still affect your comfort greatly. And, yes, sewn footbox is a better idea - though, since the zip is on the bottom where your legs lay, I don't think its that big a deal. But better to have sewn unless you're sure you'll use a down throw at home, which is probably unlikely.

The only time I've been remotely too warm in a hammock has been when we hit a muggy, steamy mid-50s night where I was using my zero quilts because it was 20 two nights earlier. And then I was not sweaty on bottom, but on top where I left the TQ off me most of the night.