Ever since owning a 6-speed Bridgestone 350 GTR, other transmission arrangements don't seem right to me.
So the CB160 (4 speeds) and the Yamaha R5 and ZG550 Vision (5 speeds) always seemed wanting, while the 350 GTR, RD350, Concours C10, EX250 and SV650S seem right with the universe.
Five speeds is ok for a car (my crummy little Yaris) but a bike with sporty flavour needs six.