I've though about a top bag, but I was hoping to be able to carry stuff, and then take the bags off for shopping(especially groceries). The other factor to consider is I have a set of bicygnals indicators, which don't come with a rack mount, only seat post mount(rack mount is a separate accessory). Because the seat tube on the boardwalk is so fat, I have the seat tube mount zip-tied to my already(relatively) small rack, making topside attachment tough.
Going through the SBS catalog, I found 3 axiom bags that might be good candidates(smaller than the Seymour), and found 3 Basils(who's aesthetics did not bug me) that were close to what I was thinking of, 2 were non-print pattern shopping panniers. Nothing, however, replaces real world experience with products though.