I'd say dont dress at all. My wife makes this mistake every time we got out camping. She uses my -40 bag and I'm in my 5 degree with just shorts on and she's bundled up like shes sleeping outside. I'm ALWAYS warm and shes consistently cold in temps that are just impossible to be chilled at in a -40 bag. I've used that same bag in colder than -40 and it still kept me warm.