Try Amsoil 5-30 European blend. I am not a dealer or in any way affiliated with Amsoil. I've been using it for 20 years with excellent results. My previous 2001 X5 4.4 would burn 1/2 a quart between 10K changes. It's possible you could be losing oil through the turbos. You could burn a quart in 600 miles without seeing smoke.

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2013 X5 3.5i M Sport
2004 M3 cabriolet SMG