I am wondering since the 4th gear is so long,.. and your highway mileage increased,... I wonder if you can get away with the X3 3.0si Auto diff at 4.44??
Might be nasty in gears 1-3 and better in 4 with manageable RPM in 5th
I am speculating because the gear/mph calcs on the web must not be right. If you look at the video and the bimmerworld.com gear/mph calc they are off by 10mph in 4th.
2002 BMW 330Ci
2007 BMW 335i