I thank you for the information-I do have decent knowledge and moderate experience backpacking. I know that temp rating is a rough guide at best. I'm just trying to figure out (short of my back yard) roughly how cold I would be comfy using the two bags together. I've used them both individually, and was warm down to to about 45 degrees. The patrol bag is pretty big-it is designed to have a big 0 degree bag inside of it, so there should be no problem with the propel getting full loft.