I sleep cold and have spent plenty of nights in temps from 5-15 in my lithium, being toasty warm, in just long underwear. I usually use a silk liner because some manufacturers (WM I think) claim body oils can seep through the nylon and damage the down insulation over time. I pair this with a neoair and a 3/4 foam pad (my backpanel in my pack) for cold nights in shelters. I agree the stuff sack would be too small for a long, I use a regular. I am 5'10" / 190# and fit perfectly in the regular, I sleep on my side sometimes and the lithium provides enough room for me to turn around in. You can't beat the features to weight ratio of this bag, great product.