I have just recently traded my 2005 X5 diesel for a 2009 X3 diesel. Both are 3.0 litre thought the X3 is a later variant with the same horsepower. I find the X3 to be twitchier, and inclined to tram track on road service imperfections. That said, it rides better, but that is probably more indicative of 245,000 k's versus 100,000. Rims on my X3 are 8.5 & 9 x 19 as opposed to the 9 & 10 x 19 of my X5. I don't feel that is noticeably smaller in the front cabin. The rear middle seat is impacted by the raised drivetrain tunnel but I rarely have 3 rear passengers. The build quality is good on both. The power to weight ratio obviously, in my case, is in favour of the X3. I didn't consider any other variants, only the diesel 3.0 as the motor is a gem. Option wise they are similar as my X5 was pretty low tech as the majority of X5 diesels are in Australia. As I did with my X5 I have fitted an Android car player, the unit for the X3 is a 10.25 inch display.

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Neil

2016 X5 3.0D
2009 X3 3.0D
2005 X5 3.0 Diesel Sport (sold)
2007 320i (sold)