I love my 3.0 but I would take the 4.6 any day of the week. Because it suits my driving style better. You are going to have repairs bills on both vehicles regardless of which one you pick or for that matter any car period. I would get the 4.6 just for the exhaust note.

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2010 X5M /// R63 AMG...Wifey's 540HP Family Hualer

2001 X5 3.0i Sport 335,448 miles & counting...
SMG M3 Steering wheel
E46 Stainless Racing Headers
4.6is Exhaust
Turner Pulleys
Afe Intake
Brembo drilled rotors
PowerFlex Bushings
Hualingan
30mm H&R Spacers rear
20mm H&R Spacers front
Bavarian Autosport High-Performance Coils
Active Autowerke's Performance Software