We both have Cumulus down sleeping bags. They are about 5 years old and have been excellent. Packing down into a very small stuff sack and very warm. Pips has a 350 model which is meant to go down to -6C mine is a 200 which goes down to 0C. They weigh 695gms and 530gm respectively. http://www.cumulus-sleepingbags.co.uk/CumulusQuantumSleepingBags.htm
We use them with silk liners and have been comfortable in temperatures down to freezing. They pack into very small stuff sacks and are easy to pack away. A good shake when you unpack them and they are ready for another cold night. They are comfortable on hot nights as well unzipping them or just pulling them over yourself when the temperature drops a bit.