The problem is, I think, that the comparison being discussed is not a true bench test of fuel consumption. 200km in a single motorway journey (if that is what this is) is, of course, not comparable to a few hundred km of mixed predominantly motorway and A road driving. As most fuel inefficiency comes from pulling this heavy vehicle from a start, or braking and accelerating, then you'd expect a series of shorter journeys to use more fuel. Saying that, I am sure I've read that there is not a huge difference between the 3.5 and 2.4 on the motorway, as 2.4 has to work harder. In this case perhaps you'd expect urban driving to be the main difference, and this would be clearer still with the hybrid model.