From 0 to 60 mph in 2.2 seconds — the Porsche 918 Spyder. A 113 miles per gallon — the BMW i8. (Both get better gas mileage than a Prius.) Sticker price capable of inducing a heart attack — plenty at the International Motor Show IAA in Frankfurt, Germany. Automakers unveil their newest lines and concept cars with an emphasis on lean, green and wow.