I'm very seriously considering getting a Timbuk2 Commute 2.0 Messenger Bag. I'm curious about just a couple of things though. I have a 13" MBP and I'd like to use a laptop sleeve that I already have in addition to the Timbuk2 case. I'd like to pick a Timbuk2 bag with a size large enough to fit my MBP with it's sleave, but small enough that the MBP fits relatively snugly if used without the sleeve. Basically, should I get the small or medium bag? (I think I can pretty much rule out the large.) http://www.timbuk2.com/tb2/products/commute-2 I realize that Timbuk2 has pretty good sizing guides but I'm looking for somebody who has first hand experience with one of these bags.