Completely UN-scientific but was out last night and the temperature dropped to about -12 Used the Banshee and slept the whole night (10:15 to 07:05) waking up feeling comfortably warm. I know that in TNF Superlight that anything below about -4 and I'm in danger of being cold -8 or so and I WILL be cold.
Thing is the Superlight is rated to -12 comfort with the Banshee being -11 i.e. very similar. In fairness to the Superlight if it had been any colder then I probably would have needed to wear extra clothes. I was wearing a merino wool long sleeve vest with cotton boxer shorts and thickish socks.
SO in this real world test what makes the Banshee feel warmer? is it just a margin of error or something else my climbing partner pointed out the price difference but that shouldn't affect the rating as its a function of the bags manufacture i.e. welded seams rather than sewn etc.