I just bought a mint 79' 528i after having several 2002s. I converted one 2002 in an overdrive 5-speed and remember that a few different gearboxs would work, but only the Gertag 235? acually produced overdrive in 5th gear. I would like to dump the revs in my new car for highway travel. I have read that the final drive ratio on the 528i with a 4-speed and the 530 with a 5 speed is the same 1 to 1. I am not looking for more power, just a quieter, more fuel efficient ride at 75 mph. Any suggestions?