Simon, I really like the 35i engine, in the 335i it sounds like an old school Nissan Skyline and basically feels more like a 4 litre NA V8 engine. But, I keep reminding myself that what we need in a 2 tonne car is torque and compared to the 35d engine the 35i has much less peak torque (although it is spread over a wider power band). I wish I could try the 35i engine before committing to a 35d, but I am not sure I will get the chance. Even at future press events BMW are likely to focus on the 35d.
Coming from a 630NM 6.3 ML63 I don't want to loose that torque (which equates directly to the feeling of luxury and effortless power). The 35d with its 580NM, which can be remapped to over 700NM is probably the better powerplant for the X6. Sadly.