I've got an Aiguille pack, and if you phone them up to have a chat to them (and then take heed of their advice) you are pretty much guaranteed to get the correct size. I took their advice when I bought mine (even though I thought that they might be wrong, as I'm borderline between two sizes) and I've ended up with a pack that fits perfectly and made to my spec. It's also lighter than the equivalent military pack.
Cheers, Michael.
Cheers, Michael.