So I decided to camp out last night, yes, on a work night. The temps went down below freezing. However, I have made a few discoveries.
1) The heavy-duty space blankets (more expensive) don't work worth a darn in combination with an underquilt.
2) The inexpensive, thin space blankets seem to work pretty well. At least much better than the heavy-duty versions. I think this might have something to do with the weight; compresses the loft.
3) The JRB Nest works much better when you shake the down to the center of the quilt before you get in.
4) The JRB Nest as a UQ, in combination with a No Snivller, as an overquilt is only warm down to about 45 degrees F. After the temp starts getting much below 45 it is time to put in the space blanket. The space blanket only seems to add a few degrees.
I did order a JRB Weather Shield for my Nest and am hoping this add's a few degrees to my warmth. I am also considering getting a 3rd quilt to use for colder seasons. I could use my Nest, and No Snivller as a combo UQ, then use a heavier quilt as a oq.