>>I have a TNF Chrysalis that I use as a summer bag and it's
>>great for that. But it's rated for 20 degrees F, which is
>>ridiculous. It's chilly at 60 F.

I'm not saying you're wrong, but there are other variables to take into consideration:

1. It depends on personal acclimatisation. Someone from Yellowknife or Anchorage might be comfortable sleeping naked at 60F.

2. It depends on the size of the sleeping bag. A larger SB will require more body heat to warm the interior. Ideally, you should get one to fit you, not just assume "one size fits all".

3. The ratings may be based on what will keep you alive, not on what will keep you comfortable. I think that would be at least possible to measure (they can measure the heat loss from the sleeping bag and compare it to the average person's metabolic requirements, for example.)

Having said that, any type of injury or illness will increase your susceptibility to cold , so a sleeping bag that will normally keep you toasty warm at -20 may not be adequate if you've been in a car accident and are suffering from mild shock. Err on the side of caution and supplement the sleeping bag with a couple of survival candles and a survival manual in the glove compartment.