My go-lite quilt is my go-to for night time temperatures of 20 degrees F and warmer. I spent 6 nights in Montana with temperatures between 15 and 25 degrees in a one man tent and was comfortably warm with a base layer and stocking hat on.
Only used a Jacks R' Better quilt on the ground for 18-20 or so nights, few below freezing. To push a quilt lower than that wear a down vest that you've sewn Omni-tape to the collar and attatch a JRB Down Hood to the vest. The Jacks say that will lower their quilts ratings 12-15 degrees, and they are old guys.
Another tip from the Jacks (JRB) for ground dwellers is to contact cement a strip of omni-tape to the bottom edge of your ensolite pad. Sew another piece to the edge of your quilt. This is best for side sleepers and done on the side your back faces. This keeps you from having the winter wind blowing up the crack of your azz. You can tuck the other side in with your arm. The "hand pocket" that Sierra Designs includes might be a good idea.
