I was given the North Face Base Camp bag as a gift, and could not have chosen a better one myself (I have a medium Timbuktu also). I first used it on a night ride, and was not sure how it would work, but did not have another bag at the time. It worked GREAT!

It stayed in place, was comfortable throughout the 6 hour+ ride, and carried an incredible amount of stuff - All the goodies you get at a well-sponsored ride, plus extra bottles and sweaters, for both me AND my wife. This is the small size bag, too. It seemed to have no limit.