I use the same. They're a very large front pannier that works well as a smallish rear one.

I try to minimize my hauling by bookending my week with hauling days. On Mondays I haul in the week's worth of work clothes, the week's worth of lunches and snack foods, and whatever library books I have to return. On Thursdays I haul home the laundry, and more library books.

I like the Ortliebs because they'er big, empty space. This gives me flexibility. There are no compartments randomly breaking up the space, and no pouches stuck on the outside that I'll never use. Except that there has to be something to protect the contents from the inside the the rack hardware. Orlieb uses a pocket for this. My U-lock or a 300-350 page hardcover book fits in it perfectly.