Timbuk2 Commute vs. Timbuk2 Classic Messenger?

-- Hope this is the place to ask! I'm just starting to commute to work on a bike, and I'd like a bag I can use to carry lunch (tupperware, yogurt container or two), a water bottle (16? oz.), phone, ipod, a change of clothes, a pair of shoes, and maybe an umbrella. I've never owned a T2 before.

Would the Commute be too small to fit all this? I'm 5'2" - would the Classic Medium look way too big on me? What's a cross strap? How well do both of the bags stay in place on bike? I have a laptop and a sleeve and like the look of the Commute's laptop sleeve, but likely won't often be carrying my laptop around with me. I'd love the smallest possible bag that can still fit everything I need for the day.

Any thoughts, ideas, helpful photo references, would be great! Thanks very much, JL