[serge1]

Welcome to the forum!
I have 2 kids (6 and 8). I have owned an alpine white 2011 X5 diesel with 3rd row, oyster seats, black interior for almost 2 years now. Let me try to give you some feedback based on categories.

3rd row: I ocasionally invite our friends couple on trips with us. In those cases, we put our 2 kids in the 3rd row. They seem to be doing fine back there, even in hot weather (there's a fan back there). The visibility to outside is not great for them, but we have done 300mi trips and I heard no complaints. I think the 3rd row is good for kids up to 10 years old.

LCI/pre-LCI: Go with LCI, you get updated bumpers and LED coronas. Looks beast.

Towing: If you going to to any towing, get the diesel. The gassers will do just fine, but the diesel is more capable (even more capable than the 50i turbo).

Fuel: My choices 2 years ago were between 35i and 35d. Both twin turbo engines. I drove both and chose the diesel due to:
-More fun around town due to high torque. It will lose a 0-60 race to gasser though.

It's the horsepower vs torque thing. Let me try to explain it without putting everyone to sleep:

Think of torque as amount of force needed to break loose a lug nut with a wrench. Like sometimes you have to put your whole body weight on that wrench to break it loose.
In the 35d, that amount equals to 425lb man holding a 1ft wrench, and putting his whole weight to break the lug nut free.
In the 35i gasser, we are stuck with 300lb man. Enough to break most lug nuts, but too light for others. Think of towing a big boat.

Horsepower, on the other hand, is about how fast you can unscrew that lugnut completely. 35i has higher horsepower (300hp vs 265 for diesel). Therefore, once the initial movement started, the 35i will propell the vehicle to 60mph faster (unscrew the lugnut). Whew..

-Fuel savings, even considering price of diesel 20cents higher than premium in the winter.
-Better highway cruiser. Mountain passes, hills, valleys - 6th gear, no changes.

Turbo/non: If you are going to go with a gasser, get the turbo version. The old 3.0i is quite a bit weak, and 4.8i yields low mpgs and bad reliability.

Colors: I have put clear plastic on the back seats to avoid them being scratched by the booster seats my child still use. The seats still look new after 2 years - better than front seats my wife and I sit, due to no protection.
Warning: the oyster leather easily picks up dye from jeans. Not easy to clean. Totally worth it though - the contrast between white leather and the rest of interior being black looks amazing. Looks really nice with soft red ambient lighting at night, too.

Choose non-black exterior. The LCI releases look much better from front and back with new bumpers. That contrast is not visible on vehicles with black or dark blue exterior.

Towing: since you required 3rd row, the vehicle will come with rear self-leveling suspension. People on this forum who do towing, say that self-leveling rear suspension an almost a must have. Really helps to stabilize the vehicle.