Page 7 of the press release on the home page for the '06 models says that with the 4.4i sport package there is a speed de-limit for a 149 mph top speed

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2006 BMW X5 4.8is Lemans Blue/Beige/Dark Maple
-Nav, Comfort Seats, Heated Steering Wheel,
Rear Airbags, AUX Input
2009 BMW M3 Space Grey/Black/Carbon
-all options