Is the GM size the same as what is referred to as "Cabine"? OP, not sure if you've seen cookymonster's thread from a while ago:
For the love of canvas (a reveal). Post #26 shows a a cabine sized herbag. A few posts down has a size comparison picture to other bags. I personally think it's a beautiful bag and a great size. Then again, I prefer larger bags because I sometimes like to carry the kitchen sink with me.

HTH!
*Edited: Oops, I think the cabine is a completely different size...but the post is worth checking out anyway. It's a gorgeous bag! LOL