We have the 2012 X5 Diesel as well as an 2011 X3 2.8. The inside dimensions of the X5 are just right for the four of us where the X3 is a bit cramped. The X3 is great for zipping around town, but for any longer journeys we're in the X5. The X3 has lighter steering and is a little easier to get around Santa Fe.

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Gone but not forgotten:
1974 2002
1986 325
1994 325
Now:
2011 X3
2012 X5 Diesel