13 is better i think, there are some bugs in 11, 13 has most of them resolved, i would go for 13 for better gas mileage, less wind noise. i will be getting one in two months.

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2013 X3 XDrive28i Sapphire Black Premium Package, Technology Pack, CWP, SAT Radio, BMP APPS.
2013 328xi Mineral Gray, Moonroof, CWP
E90 2011
E90 2007
E46 2005