Ye really does suck, look at down bags with a lot of envy
guess will have to weight save a bit more with other pieces of kit and loose some more to make it a bit more even lol
Don't despair. The Lamina frequently crops up when these questions get asked so it's definitely worth a look and I've got a couple of Snugpak bags, neither of which are that heavy. They'll never pack as small as an equivalent down bag but it's manageable. My laddie easily carried the Snugpak "sleeper lite" in a 45l sack along with a 2 man tent, food and spare clothes.
Snugpak ratings are a wee bit optimistic IME. The aforementioned bag is rated at 0C (Comfort) and -7C (Low) but I'd say it was nearer 5C and -2C. YMMV, of course as everybody's different.
Happy hunting 
Edited to add: Just remembered this, a synthetic top-bag that works with any 20" wide rectangular sleeping pad. Interesting but maybe a wee bit dear for a synthetic.
Trouble no one about their religion;
respect others in their view and demand that they respect yours.
~Chief Tecumseh~
Edited: 16/05/2012 at 17:19