A couple questions:
1) What are the lows you what to sleep in during the winter?
2) What's the minimum temp you are comfortable using the Ghost without any additional insulation?
I have be comfortable down to 10F using a Ghost (.85 fabric) + Thermawrap Vest + Down Baklava, Cloudveil Peak pants, inside a tarptent (breezily.. but not windy). We have also used the Ghost over my daughter's sleeping bag. For a few nights in a row this system has been fine. If it was an extended trip I would be more concerned with moisture accumulation and would want to be wearing a vapor barrier and have a more water resistant shell for the quilt.
I wonder if the Ghost would be wide enough over an adult side summer sleeping bag.
Of course, the ideal would be down on the inside, and the outer insulation being enough to keep dew point beyond the edge of the down quilt.