The Metropolis is huge. I'm about 5'8" and it wraps around my torso a bit. It's also comfortable when it's full. When I was still riding with mine I usually carried my office clothes, my laptop, my vast array of writing implements and various other small items with plenty of room to spare
. I also have a Citizen, and it's big enough to fit the same set of stuff *snugly*. My preferred bag before either of those was an Ivan rolltop, as backpacks are much better for heavy loads. Now, though, I use a Trash Bags Garbage Truck rolltop. It is much more comfortable than any of my Chrome bags, and it can carry quite a lot. (4-5 Cisco switches was my biggest load, IIRC)

For school, though, unless you need to bring your whole locker home every night, the Citizen will probably be plenty big enough. Just pack the soft, compressible stuff (clothes) so that it's next to your back.