Another factor I never see mentioned in a post in threads regarding gearing is the crank arm length. I've seen arm lengths vary from 160, 165, 170, 175 and more mms. This is going to also effect your choice of drivetrain configuration. The longer the arm, the more leverage you can get on it, and that will also increase the duration of any given power stroke, as well as the rpm's you turn. Is the cyclists legs powerful enough to crank a certain drivetrain setup ? And some bikes, you'll need to know bottom bracket clearances with respect to arm length and clearance to the road ? Nobody wants to stick a pedal into the asphalt while pedaling thru a turn, that might be quite a painful experience ? Might get lucky and only hear a scrape ?