I dont know... more power?! Get 4.8iS then. But again why do you need that much power for!? I mean I thought 4.4i has enough power, as these guys are saying it sounds funny but to some extent they are right... heavy duty supercharger makes the car even heavier and you know how X5s are damn heavy even just opening a door alot of people complain, they think I hide stuff in my doors! So putting extra power might need you shed alot of weight... ha you included! kidding but serious think about it... oh! again put extra $$$ for gas!.. Mine it takes 19.4liters/100km I dont know about 4.8!

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