But seriously - there's plenty of discussion on this. A lot of it's preference, cost etc. But, it's worth noting that a lot (!) of european cars have gone to 6 speeds long ago. Simple math shows that a 6 speed should be more fuel efficient. I've had mixed results with that though. The first new gen diesel we had with the Allison 6 speed trany got worse milage than the previous gen combo. But the 2008 diesel with the 6 gear allison gets amazing milage.