Due to the fact that the dead citrange tops have been cut off, I was able to weed the 4 rows of plants this morning. Ilya had mentioned that some of the plants would regrow from the roots. I had dismissed that possibility as each time I canvassed the plants their condition had declined further. That's no longer the case, as some plants I had dismissed as doomed are growing from a lower stem point.
So, I need to categorize the remaining plants into at least 3 categories: normal sized and stem hardy above the snow line, dwarf and hardy (likely under the snow), and normal sized, but only stem hardy under the snow during our sub-zero temperatures. As they grow out, the stem position where the new growth originates will show how stem hardy the plant was.
Unless the plants regrowing from low positions are unique in some way (monofoliate, etc.) they might not be included in the elite group of super hardy specimens for further breeding. They do warrant preservation and further evaluation, however. They might be better suited to zone 7 growing conditions.
I assume that the F1 hybrids are dead, and the under-snow hardy plants are F2 plants.