I agree with Kevin... the Ghost can be used to 32F thought I am not sure I qualify as "thin" being 5'10", 180lbs. I have been mostly comfortable with a Ghost, medium weight base layer, GoLite Snow Cap, and wool socks. Mostly comfortable because I am a side sleeper and by the morning enough of the down has shifted so I have a cold spot where my hip is at the peak. There are four things which would eliminate this as an issue: sleep on my back (nope), 1-2oz overfill (costs money), wake up and shake the quilt to redistribute down (that's cold), or place some clothing item (like my hiking shirt) on the top of my hips.
I have used the Ghost down to 20F with a silk liner + dwr bivy, or with with a thermawrap vest, MH tempest gloves, and primaloft socks.