You won't be disappointed in the 50. Huge step up in performance from my old '01 4.4 X5, and much easier to live with as a daily driver than my '04 M3 convert. The 8-speed transmission is great and there is always plenty of power on tap. Getting a legitimate 20mpg on highway, 14-16 in the city. My only regret is getting 3rd row seats and not adaptive drive. My 4 and 6 year-old complain about the 3rd row being too small...
Comfort seats are worth the money.

Also, I am assuming you would be looking at a September build, which will have some bonus features relating to iTunes. There are continuing rumors of software updates which will dial up the boost and performance, so hope to see something for the 50 soon.

Good luck with your search. At work, so no pics to share other than the Avatar. Found silver/black to be a nice combo.

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AtlX
2014 X5 35i M-Sport While/Black (wife)
2013 X5 50i M-Sport Silver/Black
2011 X5 50i Silver/Black (retired)
2008 335i Convertible Space Gray/Gray (retired)
2004 M3 Convertible Blue/Gray (retired)
2001 X5 4.4i White/Black (retired)