Yeah, preface lift Z4 with 2.5 and 5-speed manual revs that high at 100kph. I don't know why BMW didn't install the 6 speed on the early 2.5, though the 6-speed SMG was available as an option. I've actually hit the rev limiter in 5th gear on the Autobahn, a 6th gear would be a nice addition. I'm not sure what would be involved in swapping out the 5-speed for the 3.0 6-speed, I suspect the drive shaft, bell housing clutch/flywheel may need changing too. Several years back I remember reading where 2.5i owners in Germany were swapping the rear diff with 3.0i owners.
The 2.5i 5-speed manual came with a 3.46:1 rear diff while the 3.0i 6-speed came with a 3.07:1. The 5th gear in both transmissions are 1:1.
In the US (likely Cananda?) the sold date or date of manufacture is not the car's model year. There were 2003 Z4s sold in Oct-Dec of 2002 and are labeled 2003s. In the UK it seems the car's sold date becomes the car's year, hence 2003 Z3s.
