In reply to derek the dragon:
> (In reply to Darkskys) Vango sherpa 60-70 litre or similar. Mainly for D of E and walking trips
I'd suggest having another look at the size of your pack, I used to use a 45 litre Berghaus Arete and now use a 38l Osprey Mutant for everything, up to 5 day solo mountaineering trips. I have the tent on the outside on one side and rollmat on the other. A lot of people buy the warmest sleeping bag they can find too, which takes up loads of room in a sack and is usually left half open. If you are going to carry clothes with you, why not wear them at night and take a lighter sleeping bag?
What I'm describing may be a bit different to how a DofE exped is run, you may want the extra clothes and space for other comforts?