how cold can I expect it to be before i...
how cold can I expect it to be before i start to lose warmth (if wearing alone?)
Probably low 40s.
Depends how windy it is and how active you are. I've worn these alone for XC skiing in the upper 20s and been fine - on a still day. Breeze cuts right through them though, so if it's breezy Angus is probably on target, 40s.