I don't really agree with you. Sure the Diesel is a great engine, but the Petrol weighs 160kg less, so it is going to be a lot sportier to drive. Besides, at higher speeds the Diesel will definetely fall back, as all Diesel versions do. Of course economy and torque-wise, the Diesel is far ahead. Stil I would take the Petrol engine because I like sporty driving and above all, I love V8 petrol sounds :)
Obviously I can't afford the car, I have an old D2 A8 4.2 (from 94, the D2 is still the best looking model :)).
Please excuse my orthographic mistakes, I'm not a native.