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Another option is the winter sock.
They were very popular at the 2013 Colorado Winter Hang.

http://farm9.staticflickr.com/8324/8441561923_dde4ac0898_z.jpg
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I only use a 20 degree UQ with 2QZQ breathable UQP in winter.
My TQ is a 5 degree SB
The trick is sleeping in insulated over clothing.
You can also use the hot water bottle trick.
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