I use my Saddleback bag (9" D) for most of time and my Rickshaw commuter (4.75" D) on rainy days. I want to get a 256 (4" D), but it may be too small for my body frame (6ft1 and 195 Lbs). To be honest, the Rickshaw looks kind of small on me.
Nice brief review you put on the youtube! I really think Dave should redimension the medium satchel. It can't fit a 13" air, a regulate 1" binder or notebook nicely. Small for 10" or lessMedium for 13" or lessLarge for 15.4" or less