just since people are spruiking about how this dpf stuff can ruin the running cost difference between the diesel and the petrol - I thought I'd put in that most importantly, the diesel still uses less fuel, and is therefore more sustainable and a better option in terms of your carbon footprint.

For me, thats the important thing.... not the cost. If it was really the cost that concerned you, then you'd be a lot better off driving a nice old car and not a new one.