Fuel comsumption has dropped I have noticed. I would say it has almost doubled, but if gas in your area is cheaply priced who cares. I wouold say my sad 0-60 time has gone from 11sec I believe they say to 8-10secs (human counting here).
One more thing your engine will get a little hotter, which might be good for those of you drive your car likes its a M3, meaning you hit 5000+rpm freqeuntly. Moreover, the heater get hotter too.
Mad E30 lover