In reply to Richard Carter:
Lowe Alpine used to make a decent very small sac, also Exped too, I think.
I have a Gourdon 25 and a 30. I think the 25 is a generous 25 and more suitable for that type of sac. The 30 is OK but maybe just a tad big for such a simple design - hangs low and back a bit, proportionally fat.
The 25 is a bit better proportioned, imo. It may not speak so highly of me ...