More gears are advantages in vehicles that have engines that develop their HP at higher than average, RPMs. Spinning the engines to gain HP for bragging rights it something the Japanese are prone to do. The problem is the torque is poor where needed in that type of engine, thus the need for more gears to keep the engine in the torque range while starting and climbing grades. Drive a 4 cy Camry, it exhibits good HP but has piss poor torque at the proper RPMs. That is why they are slugs when it comes to climb a grade. Six speed and above trannys are generally double overdrive for economy as well, but not worth much under load..
mike