[fragdude]

As I understand it, the 5 speed transmission has shorter gear ratios for better acceleration (why some people prefer to put 911 engines in a 5 speed car). The 6 speed has gear ratios that are identical or very similar (I think, I read that somewhere) to a 911. First and second are "long" which is nice for auto X where you generally just stick in second, but can have a wide range of speeds, 3-5 are "short" which is great for high speed acceleration (I beat an e46 m3 on the highway from 65-130 probably because of this) and 6 is the cruiser/top speed gear.

I don't remember where I read this though...