I'd go with the naturally aspirated engine. It might not be as powerful but you said that speed isn't the top priority. Naturally aspirated engines generally have much better longevity than turbo engines, especially when it comes to BMW engines. BMW still hasn't quite figured out turbos like Audi and Porsche have.

Even though the 2010 with the naturally aspirated 3.0 engine is older, it'll be a lot easier to work on since you won't have all that turbo plumbing in the way. Plus you won't need a warranty as badly with a simpler engine.

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2003 X5 4.6 | 2000 540i Touring

Formerly owned:
2004 Range Rover | 2000 M5 | 2000 540i/6
1995 750il | 2003 Mercedes S500 | 2003 540i/6