I've got an old NF Blue Kazoo, which I use in spring/autumn and for me is ok down to about 0C in thermals, and -5C with my downy over the top and a hot water bottle to warm it up. It's great for what it is, but not so good in cold weather for me.
I've also got a Mountain Equipment 1250 Glacier bag which I bought for an expedition last year but it didn't happen unfortunately. The bag has a comfort zone of -12 to -20 with a 'good nights sleep' temperature of -25C according to ME (whatever that means). I've used it at -10 or so a couple of times and it's very warm. Haven't bothered using it much more than that as there's no need, it's too warm.
I think I've come to the conclusion that I need to sell the ME bag (offers around £350*) and get a bag that does the -5 to -15 range (chilly winter/spring alpine bivvies, and comfortable Scottish winter camping). I want down, I want it to last, I want it to pack down small and weigh little, I have no idea what current fabrics are good/bad, and have even less idea about if waterproof down is worth having or not. What's around at the moment that's good? Anyone selling something second hand that would do what I need? I'm only 5'7" so want a short bag to save weight/space. Preferably a zip on the left as you lie in it. And recommendations welcome!
*Regular size, green, left hand zip, used for 5 nights in the alps (always with a liner). I can't find the RRP, but Cotswold have it for £540. Cheapest I can see new is £405 + p&p from abroad. Email me if interested. I'll put an ad up at the weekend. More info here.
http://www.mountain-equipment.co.uk/glacier-1250