With the additional low end torque of the BB, the 16 is probably overkill. The 17 is for people who want to leave all the other cruisers at the light. The 18 is more for people who don't want to be looking for another gear. With the 18, I sometimes miss the really quick starts, but don't feel like I need a 6th. 5th is more like an overdrive. I don't use it except over 55-60. I still have plenty of oomph even 2-up.
