I just got back from a trip to the north woods in WI. I used my quilt for two nights with temps in the low 40s to low 50s, and very damp air. I slept under a tarp and used just a groundsheet.
I was completely warm and comfortable, which was expected because I have a 20F quilt, but I was also not too hot. The beauty of these quilts is the adaptability to different temps. If you get too warm, you can open the foot box for venting, and because of the baffle style (Karo) you can easily shift the down off the top of you. If it gets chilly, its really easy to move the down where it's needed.
Check out this thread:
It started as a silly Chaff thread, but there are some good photos and I've written more on my quilt. Let me know if you have any questions!