Haven't used their quilt liner, but I can offer anecdotal experience with 100-wt fleece. I use a $3 WallyWorld fleece throw as a temp booster in the winter months with my poncho liner top quilt. It buys me about ten degrees' comfort.
Assuming that the liner does the same, it should be warm for most folks down into the mid-sixties (since most folks need a quilt starting around 75 F).
Mind you, completely unscientific and based on an experience with a different product, but it's what I've got...
Hope it helps!