Here are some shots of my Carradice Barley that I use for commuting. It has plenty of room for my tools, spare tube and repair items, spare batteries and parts in the side pockets. In the main compartment, I can easily fit a dress shirt, t-shirt, underwear, wallet, cell phone, lunch, eye glasses and more. I would be tempted to get a Pendle if buying another Carradice, but the Barley will hold everything I need 99% of the time. If my bag was larger, I would just be tempted to carry more stuff that I don't need.

The main reason for more space (for my purposes) is during spring and fall when temperatures vary widely through the day, or when rain is threatening and I want to carry a rain jacket for insurance. This time of year, my bag is usually more fully loaded in the afternoons when I have to carry home my vest, arm and leg warmers, long-fingered gloves that I wore in the mornings when it was much colder.

BTW, you can find the best selection and prices for Carradice bags at the British websites like Wiggle, SJS Cycles, Ribble, etc., as well as directly from Carradice. They also have information on the volumes and weights for each bag.

Currently I am using an Acorn Medium-Large bag on my main commuter, a Salsa Casseroll. It has about half to two-thirds the volume of the Barley, but I have made a conscious effort to lighten my load. My commute route is very hilly and I can average 1-2 mph faster with the lighter bike and bag.