[QUOTE3 things to
NEVER compromise on
1. anything to keep you dry (waterproofs)
2. anything you wear on your feet (boots)
3. anything to keep you warm (sleep system, warm kit) ][/QUOTE]
Personally I wouldn't attempt that without a proper bag that was up to the job. Saving a couple of hundred grams for no sleep or worse isnt really a great gamble. I'd rather be knackered and have a nice warm bag to get into and a good night's sleep with slightly heavier kit...
Both excellent advice. You can have it cheap, you can have light, and you can have it effective/durable/warm - chose any two. The Venom is rated on the Go Outdoors website down to plus 5 degrees. Sleep a litle cold and its all goes pearshaped (depending on when your going), and that might be bad news. Minus 5 might be OK for a rating, but down is going to cost you - the Rab Ascent 500 is about £200.
But if your walking a long way, every extra gram is going to feel very heavy! Try second hand (perhaps the classifieds on OM), or possibly the Rab factory shop - you never know what might come up.