I finished my 20 degree MYOG Momentum and XP oversized quilt .... the quilt weighs in at about 17 oz.
I used a double layer of XP from the chest down and a single layer of 2.5 oz basis weight XP from the chest up. Since I always carry an insulated pullover anyway, I figured I should integrate it into my sleep system.
I've made a number of quilts in the past and my problem always seems to be that I try to make the quilt as small as possible to save an ounce or two of weight. Not so this time, since I was reducing the amount of insultation in the top half of the quilt I had some room to increase the overall size and still stay below the weight limit of my current sleeping bag.
I made the quilt oversized, 58 inches x 84 inches so I would have plenty of room to snuggle, tuck, etc. In a pinch, I could probably snuggle two into the quilt, but I'm a big guy and I like to roll around a lot at night. I don't always carry a Bivy, so keeping the momentum shell unbroken was also a priority for me.
I have a problem of getting cold in my 32 degree bag here in Texas, backpacking in the winter, there are nights that drop into the 20's unexpectedly. That, and with high humidity levels, can lead to a uncomfortable night ( of which I've spent a few), when my bag didn't loft all the way due to dewfall, or the temp just pushed the limits of the bag.
No matter how you slice it, however, I've still shaved 7 oz off my 32 degree bag and dropped the temp rating by at least 8 degrees, and switched from a down bag to a synth quilt (less expensive, less sensitive to humidity and dew). This pays for the weight penalty of the homemade bivy I carry sometimes during the fall and spring for bugs.
Not bad if you ask me.