If I am not wrong, the fact that the X5 is way heavy makes all the difference between the two motors. The gasoline feels anemic in the SUV. The diesel with all that extra torque will be noticeably better. Like huge difference better. In the car, the extra torque wont be nearly as noticeable as it is in the big lumbering SUV. The E9X is kind of light, so even the 335i stock is almost on the edge of what the wheels can handle you really get on it. Throw in the 335d motor, and I am sure the torque makes a difference to a point, but the past that point, it just results in wheel spin. In the SUV, it makes real difference because of the extra weight.
My tuned 335i has as much torque as the diesel. I notice its punchier than stock, but I can't tell at what point the extra torque goes to waste as it is so easy to start spinning if you realkly get on it, and once you are spining, you wont feel any extra torque you pile on past that point. So the results wont seem as dramatic as in a vehicle likean X5 where even with the 428tq, I suspect you are nowhere near the limits of the wheels ability to take it. That thing is heavy so you will use every pound of that torque and feel the entire difference as opposed to the car where you probably use only half the extra torque before the tires start giving up and you can't feel the rest of it. Just my opinion. What do you guys think?
On a funny note, I drove the new ML350 with the older V8 at the Mercedes launch event before the 335 came out and liked it so much I almost got one. I felt it put the X5 to shame. It really did. The new X5 though gets it back. I felt the SUV had almost leveled the field with cars and the damn airmatic suspension in the ML is something else. So comfortable and literally glides on rough pavement yet doesn't wobble and roll like a boat on the curves. But then along came the 335 and the game was raised 10 fold. I can't even imagine getting an SUV over this car.