when insulation is required inside a bivi bag, i suggest a looking into a Blizzard Bag
If it is an emergency, I would have to vote for the Blizzard Bag. I carry the hunter orange and a plb. I hate the idea of a search prior to the rescue. In a non-emergency, I would leave it in the pack and use the Goretex Set and the military poncho. I pack as heavy as I can stand. You won't stay in shape unless it hurts.