Ase, come on man, if you are concerned about mpg and not hp then an M3 is not for you....................
If you want both then get a 335i and up the boost like crazy with a chip too..............
Bottom line is performance and mpg do not get along.......
Unless you get a Lexus GS450h hybrid.......but then is an electric car something that you really want???? And it still doesn't handle like the cars from Munich.................