I had a 2008 3.0si for almost 6 years with no major issues.
Few factors to consider:
1. I believe 2010 3.0 is a I-6 but not turbocharged while 2011 3.5 is turbocharged with more power and better acceleration. I would think a non-turbo will be more reliable though.
2. 3rd row seating is good enough for short trips with kids. It came handy when I needed it.
3. In the U.S. diesel fuel costs more which offsets higher MPG.

Hope it helps.

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2011 BMW 740i
2011 Toyota Sienna Limited
2008 X5 3.0 Space Gray (sold)