Oh, man - just do it! You will love every minute of it. I don't take my X5, but I was at one last year where one driver ran an E53 and she and the instructor had an absolute blast. Definitely wasn't the fastest car on the track, but I bet you'll be very pleasantly surprised how competent the vehicle is at speed.

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2013 X5M - Sapphire Black
2006 X5 4.4i - Sapphire Black
2002 M3 Euro - Alpine White
2003 M5 - TiAg
2003 M3 - TiAg
2010 535i - Deep Blue Metallic
2007 530i - Deep Green Metallic