My previous sleeping bag was a Feathered Friends Lark:
. This is a really high quality bag, so my standards were high. But, I wore mine out relatively quickly, not due to a problem with the bag, but just due to my own body chemistry. My sweat destroys down rather quickly. I know this because Jess still has her Feathered Friend's bag that she got only a little after I got mine, and it still looks good.
So, I didn't want to spend that much money again knowing how fast I'd wear it out. I wanted something cheap, and versatile, but I still believe that my sleepingbag is likely to save my life, so I wanted it to be ridiculously warm, and I didn't want to give up weight or bulk.... I also wanted a pony.
Well, it turns out that sometimes you can have your pony. Via backpacking light I caught wind of a new company Enlightened Equipment, making cold weather down quilts. From them I got an 850 fill overfilled 5 degree medium taper down quilt. The owner is revising quickly so that model is no longer available, but it's similar to this one: http://www.enlightenedequipment.com/?product=revelation-850dtorried
WarmthBased on my reading quilts can be drafty, so I was really worried about being cold with it being a quilt, which is why I got a 5 degree quilt (the lark is rated to 10F). So, I also picked up an MLD bivy http://www.mountainlaureldesigns.com/shop/product_info.php?cPath=22&products_id=30 . I got it in silnylon with a mesh facepanel. This gives me a bit of a warmth bonus, and works super nice in powdery snow as it keeps the snow off the bag.
I've now been using this bag for a couple of years. It Is warm, very warm. For those who haven't used quilts let me clear something up. This is not just a flat quilt like for a bed. It can be used that way but it can also be zipped, snapped, and drawn up so it hugs you almost like a sleepingbag, except it has no hood, and no bottom. In a sleepingbag when you roll the bag rolls with you, but with a quilt you roll beneath the quilt. This is a big difference, I find it an upside but not everyone does. Also note that it makes liners a touch more annoying since the liner will turn with you and my try to pull the quilt with it. The lack of a bottom is also what makes quilts comparatively drafty. It comes with stretchy cords to run under you sleeping pad to lock out the drafts, personally I hate them and don't use them. Usually it's not a problem and when it's *really* cold the bivy holds everything close to me so there's no gaps, as well as providing an extra wind barrier. I used it in this shelter for example:
Sierra winter SAR training
I almost never use the bivy though, and consider it cold weather gear. I should've used it, but did not recently when Jess and I slept in the truck together at -25F. I had additional clothing on of course, and the truck probably adds 10 or more degrees as well. That said, lets say it's equivelent to -10F... that's damned good for a 5F quilt, even with some extra clothing.
Baffles and leaks
The biggest flaw is that just like the Lark the down doesn't stay in place well enough. I notice that the new model claims to have improved this, but it definitely is an issue. I've often found myself cold and realized that the part of the bag in the center top (about where your chest is should you lie on your back) has no down in it at all. I regularly have to shake the down back into that part of the bag. There's always tons of down at the feet though, so no worries there. As a heads up though note that the bottom doesn't *fully* seal, there's about a quarter sized hole left after you draw everything up. If you shove virtually any piece of fabric down there though it's trivial to seal it off. In colder weather I often use my down vest.
Picture from the JMT
Note that mine is a very unusual baffle design that I haven't seen many places. It's sewn into large squares about the size of an opened hand, but the corners are unsewn. This allows down to move from anywhere, to anywhere, but not super easilly. It's an interesting idea, and I have to say that when I washed mine for the first time recently it fluffed up and filled the bag with no trouble - still, I get the feeling it was an early design and I'm looking forward to something that keeps more down over my torso.