If you look at Western Mountaineering specs as their temperature ratings are widely considered conservative, you'll find:
Megalite - 4" loft, 30* rating
Alpinlite - 5" loft, 20* rating

The luxurylite, with 4" of loft, should be comparable in warmth to the megalite (30*). So, perhaps not 20*, but at least good to freezing for most people.