I know you were asking for other suggestions but thought that I'd add that I have the mid-sized Chrome rolltop and have had a good experience with it. It does not block my over the shoulder "look backs" except for when its packed totally full. I went to the LBS, brought as much stuff as I expected a heavy commute would be, and test rode the messenger bags/packs. Look for a suspension system (pack straps not bike forks) that works well for you. Anything can have a water proof cover put over it.