First off, the EPA way of testing fuel consumption is flawed. That's why you often get wierd numbers, such as better fuel economy for an automatic versus a manual.

Secondly, lets not start the whole "Why diesels" debate again. Diesels have a much farther range on a tank of diesel. They have more useable power in day-to-day driving. And even if you feel like thrashing the car all day, you'll still get respectable fuel consumption numbers.............unlike petrol. Thrash an X5 3.0si for a few hours non stop and then tell me if you can get better than 9 miles to the gallon.