I never wished for more power with my 2003 3.0 X5. If I wanted to go faster, I wouldn't have been in an X5, I would have been in something that didn't weigh close to 5000 lbs.

But since the topic is reliability, I don't think that the weight of the X5 caused a decrease in reliability of the 3.0. And if I was going for high miles, I would pick a 3.0 over a V8.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue