Hi falcon5000,

How about a tough and robust, 5F, -15C rated down sleeping bag with built in water proof base with integral stuff sac and weighs in at 2.1 Kg. (similar performance to the Wiggy's bags in terms of weight and temperature rating but 1/3 the price, new ones can be had for around £40 $80)


The good old British Army 58 Pattern sleeping bag (first produced in 1958)

http://www.dubora.com/index.php?main_page=product_info&cPath=12&products_id=566

Combined this with an 800 gram British Army Goretex Bivi and a 700 gram Alpkit Airic self inflating pad and you have a very effective sleep system weighing around 3.6Kg 8lbs which is waterproof and usable down to temperatures below -15C for around £100 $200).