There's a difference between comfort level and "stayin' alive" ratings. I've seen a Coleman temperature chart of sleeping bag ratings, and there was a "comfort zone" that was above the minimum rating.
Last year I made it out alive with a 40 deg F bag where overnight temps were somewhere around 38 deg F. I wore poly underwear/socks and a wool beanie cap while I slept. Keeping the head warm can really, really help.
I tried out my backpacking bag along with a cheapo car camping bag before I set out on my backpacking trip. I took it to a campground in Tahoe where overnight temps were around 40 deg F around Memorial Day. I might have been comfortable with the 30 deg bag when it got to around 40 deg, but when it warmed up to 50 deg in the morning I on the verge of sweating. With the 40 deg bag I felt a bit chilly but not too bad, but it felt better as the temps rose in the morning. I guess if you have a zipper you might be able to regulate it in the morning. My backpacking bag was actually zipperless.
Post Edited (07-16-08 11:21)