I've only got a five speed, but I hear the same thing from others with 6 speeds ... great for 140+ mph driving, but rarely used any other time and a bit of a waste. Mostly there to differentiate the S from the non-S.
I wonder how much low end grunt your car might have with a 5 speed on it with lower gear ratios
Should I upgrade to a 3.4, I'm going to attempt to keep a 5 speed tranny in my car.