I've had my bike sitting idle waiting for me to pull the 6 speed box apart and reseal it. I previously used a 4 speed close ratio box when racing, which was excellent everywhere except off a clutch start. If you only have four gears and they are close ratio, you can set the overall gearing high and still have legs at the ends of the straights, or you can set it low and come out of the corners faster but run out of puff towards the ends of the straights. With 6 gears, the ratios are usually closer, but as you raise the overall gearing they spread out to be similar to the 4 speed ratios, but with two lower gears. That means, that if you are racing, the ratios are more appropriate for most situations. With the 4 speed close box, once you are rolling, it is superb. With 5 gears, you can fit a lower first gear to get you mobile. Once you are rolling, you never go back to first gear anyway. In my case, the 6 gears will only be of real benefit on the first two corners of a race. If you can race-change off the start line, that is much faster than revving the tits off the motor, trying to get mobile with a 4 speed close box. When I race, I usually go around the first two corners as fast on the first lap as I do on the last. If you are up front after the first two corners, life is much easier. What you lose on a slow start, is very difficult to regain.
I don't know how you would use a 6 speed close box in a Commando on public roads, unless you were drag racing from traffic lights.
