You ask a lot of questions that I feel either can not be answered, or can only be answered by you.

I did some googling, and found this Bag rating , which may or may not help you. I found this part of it most interesting, "...There is no universal standard for rating sleeping bags. Ratings vary according to manufacturer. How a bag performs greatly depends on its insulating material, construction and loft. When selecting a temperature rating for a sleeping bag, be sure to consider the following..."