I’ve had both a 220d and 218d Gran Tourer as long term hire cars in the last year. The auto is really smooth and suits the car. I haven’t tried the 1.8diesel engine, but the 218d with less power was a good chunk less efficient than the more powerful 220d. Its quite a heavy car and benefits from the extra torque allowing it to stay in the higher gears.
On a steady motorway run the 220 would get up around 60mpg, the 218 was down in the low 50s.
I would also recommend the ‘luxury’ spec rather than the M-sport. The M-sport had low profile tyres and an uncomfortably hard ride, the luxury was more comfortable with better seats IMO. I don’t think that a 7 seater MPV is really the type of car that benefits from 18″ alloys and bucket seats 🙂
For me the big advantage of the auto is how much less hassle it is, especially in stop start traffic. I have had lower back pain for a while, and also find an auto takes away stress on that too.
EDIT – the 218d had a 150bhp ish 2 litre engine. The 220d had a 195bhp ish engine.