Here's another significant comparison: The new Z4 SDrive28i (with that 4-cyl, 240hp engine) gets 34 mpg on the highway. The similarly-marketed and popular Mazda Miata is over 800 pounds lighter and has 73 fewer horsepower... yet it gets only 28 mpg on the highway
Turbo+DI 4-cylers are becoming a tremendous
competitive advantage. And their horsepower will only increase. There's really no reason why the TwinPower 4 can't produce *300 hp* with a 3rd-party tune (I had options up to 315hp for my GXP), which means makers have plenty of room to ramp those numbers up over time (while preserving gas mileage).
I know nobody's going to agree with me, but I predict the TwinPower 4 series is going to replace the N55 within a few years.
(source for stats above: http://www.foxnews.com/leisure/2011/...-z4-sdrive28i/
2012 135i convertible, DCT, Black/Beige, HK, Prem, M sport, no nav.