I test drove both multiple times before going with the 550. The $4500 difference was a comfortable one for me to go with the 550. When cruising, you can't really tell the difference in terms of power between the N55 and N63 engines. It's really in the acceleration that you feel the punch with the N63 engine. I have to say the N55 does have that sportier feel especially while cruising while the N63 seems too smooth. That's just my observation.
2013 BMW X5 35i
Alpine White | Cinnamon Brown | M Sport
2013 BMW 550i
Titanium Silver | Black | M Sport
Last edited by Decboy; 01-19-2013 at 10:38 PM.