Having spent 4 nights using my Katabatic Sawatch I can say it is definitely a keeper. Although the lowest night time temp was only 27 degrees, I am confident that when combined with the down hood and on my DAM, 15 degrees shouldn't be a problem. At the other end of the spectrum, a warm front moved in the last night (along with a much lower elevation - 6300 feet), bringing a night time low of 55 degrees, and the quilt was comfortable, just a bit on the warm side but it was very easy to vent. Breathability of the fabric seemed excellent with no clamminess at all. For reference I was sleeping in long silk underwear all 4 nights and wore no hat, sleeping in a mesh walled tent. It was very windy every night (and day), making for slight breezes in the tent but I felt no drafts. I did not use the cords to attach the quilt to the pad as I found it unnecessary just relying on my DIY elastic straps to hold things together.
The shaped form of the quilt is much more comfortable than a "flat" quilt that is wrapped around you. I have used a flat quilt before and have a Golite Ultra 20 as well, and while the Ultra 20 is also somewhat "shaped," the looser fill of the chambers isn't as effective in the quilt keeping its shape. This shaped aspect of the Katabatic quilt really helps to keep it wrapped around your torso and shoulders without having to resort to the use of ties or cords in mild temps. IMHO, the collar would function more effectively if it was sewn so that is couldn't just stick out of the top of the quilt suspended on the edge of the top baffle and was more "tucked" back into the bag. If you are on the border of a regular or large, it does add a couple of inches of length so it is something to think about. Once you fasten the snap and pull the drawstring however, the collar works very well as designed, sealing in warm air without an unnecessarily tight cord. The only other feature I would have liked would be a hang loop on the inside and outside of the footbox. In fairness, the top drawstring cord works equally well and may in fact distribute the weight on the attachment points of the shell better but I always like more options.
Right out of the stuff sack it really lofted up fast. My hiking partner was VERY impressed and he was using a WM UltraLite Super, one very fine bag. The fabric and color of the two bags was very close in appearance and feel and we both agreed that the sewing quality was equal. I couldn't tell if there was a difference in down quality between the two, but the Sawatch had another 1/2 to 3/4" of single layer loft and seemed to have more full baffle chambers as well. This would make sense given that the UltraLite has 1oz more down but more volume to fill. He is VERY meticulous about the care and use of his gear, and his bag only has some 10 nights in it, making the difference more legitimate and not a function of a dirty or mistreated bag. Between the new quilt and Kookabay DAM he was admiring, I felt like I ought to sleep with one eye open.
Unfortunately it won't be until Fall that I can test the 15 degree rating, but I feel that it should be realistic given my assumptions above. Augmented with down clothing and hood I see 0 f a real possibility and hope to use this as my "light" winter bag - now that's versatility. If I could have the one perfect all around quilt for my use, it would be something between the Sawatch and the Palisade, say a 1.75" baffle height and 12oz of down. A Palisade with a 2 or 3 oz overfill would be a real contender at 19 - 20oz and a guestimated lower temp of 20-25f and that is something I thought long and hard about. I have to admit that having used the Sawatch I am still thinking that might have been my "perfect" bag, but the extra 3 or 4 oz between the overfilled Palisade and the Sawatch is very nice insurance against an unexpected cold front for the weight of a wind shirt. Moreover, not having seen a Palisade, I don't now if it would benefit from an overstuff as much as I am thinking. I don't feel you wouldn't gain a great deal by adding more down to the Sawatch - it is that full. Curiosity may get the better of me and I will get one anyway even though I have basically new WM HighLite I was thinking about making a quilt out of.
You will not be disappointed with the quality of either bag's materials and construction. Unless you want something really custom, Aaron at Katabatic really has built a better mousetrap in the quilt/variable girth bag category, and I have not even tried the patent pending bag to pad attachment system. The only question is which one and to overfill or not.