My '87 325 with an ETA gets 25 in the city and 30+ on the highway. I like my ETA, however I know the "I" is more spunky. The ETA I figure is a beter daily driver while the "I" is better for performance. I also use Redline Oil everywhere in my car: engine, tranny, rear end, and even the power steering system. The Redline products help my gas mileage. Oh yea, I dont do the speed limits... I generally do 70 in a 55 and 80+ on the interstates... I dont drive my car all that easy and it still gets that good of mileage. I use only regular 87 octane fuel too.
If you are looking for a car to tweak and make into a rice burner eater.... definetly get a E30. You can do so much with them. I plan to eventually put a 2.9 liter M20 into my E30.
FYI, bmw has made 6 cylinder engines for a long time, since the 30's I think. I may be wrong though. I do know that BMW also made airplane engines in the early years and during WW2 they made Jet engines.
Not bad for a car company. Later.
Aaron