I used a 30 degree Katabatic quilt down to 16 this winter, supplemented with puffy pants and jacket. So it's doable, but it's not ideal. For me, it's generally not comfortable sleeping in a lot of clothes and I would wake up every couple of hours feeling like I needed to readjust. If you are going to try extending your quilt's temp rating, you'll want to be sure you're getting a comfort rated quilt - some manufacturers hand out pretty generous temp ratings.I want to go overkill with the rating, but my wallet says otherwise. I appreciate your feedback, I’m thinking of maybe supplementing a lighter quilt with the puffy/ puffys I carry anyways. Just planning on a serious trip this year and don’t want to be miserable as I usually am in a mummy bag. How tough is the Xtherm, and do you carry a ground mat for it? I’ve read good reviews, but a buddy of mine says he’s gone through a few of them.