I would pass on the '07 as it was the first year. There are many that are just fine, with few problems, and you may find a nice clean one; then you would have to decide. But if I was staring to search, I would look for an '08 or '09.

The 3.0 was adequate in the heavier E70. I liked the 3.0 in the E53, but would want to make sure it had sufficient power for me if I was looking at an E70.

3.0 twin turbo (35i) in later years is the best combination IMO. You are looking at more money then.

Diesel is something you either like or not. It is a different driving experience. Not so many revs, not the same engine sound, but lots of torque. Recommend you drive one and decide if you like it.

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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