Where I live in South Carolina the dealer is selling more sdrives because it doesn't snow here and they can order them and keep them under $40k which is hard to hit with a 3 series. The EPA estimate is fairly close but maybe a little generous and you'll probably get about 22 in true stop and go city driving. I've gotten about 31 on true hwy driving but well above the speed limit. S drive is probably about 1 mpg better in town as much due to weight as mechanics.
1995 325i,1996 328ci,1997 528i,1997 Z3 2.8,
2001 X5 3.0,2001 330i Conv,2002 M3 Conv,
2003 M3 Coupe,2004 M3 Coupe,2004 Z4 3.0,
2004 X3 3.0,2007 X3 3.0,2007 335i Conv.,
2013 X1 28 sdrive M Sport, 2014 M235 on order