Unless you have anti-freeze in your viens, imagine for one moment the difference between "comfort" at + 2 degrees and even -4. Then contemplate minus 20 degrees, in a bag that light.
I think you'd be long gone by then!
Have many of us even been in conditions of -10 or under?
That's what it was on top of Kili before dawn, likewise at the climbing hut below Mt Kenya's 2x summits.
Don't get me wrong, I love Rab kit, I have an Atlas 600, but these sorts of figures are just rubbish.
EDIT: Just look at that! -10.6 FFS how stupid and misleading is that! Is that when the crash test dummy shattered? Point anything of a degree is indicative of some stupid figure plucked out of thin air by some 1/2 baked marketing dept.
Where do you get -10.6 from?
All of the new RAB bags are EN tested so I doubt any figures are 'plucked out of the air'. Thats the way the EN rating system works comfort, limit and extreme ie minimum temp before death!
EN ratings certainly arent the be all and end all when choosing a bag,(a really good mat would be a good start as well and knowing how cold you sleep) but at least there is an industry standard now so that people can no longer pluck figures out of the sky! 🙂