The mpg quotes are controlled environments... All cars are judged on the same basis...
If one car is achieving 20mpg and one is achieving 40mpg... The figures may go up and down depending on your "version of combined" but the outcome will still be the same. the diesel will drive roughly double the amount of miles the petrol does regardless of the actual figures.
Hope you can appreciate that.
No, I cannot appreciate that.
I have driven many BMW diesels and not since the E39 530d have I driven one that I've been able to comfortably get near the quoted figures with. A useful benchmark is the fact I often drive from Devon to Hampshire - a mixed route of dual carriageways, A roads, etc.
In every petrol BMW I've driven the route on, and the E39 530d, I've managed to acheive the combined consumption figure (And in these cars, I've managed to acheive the extra urban figure on mostly Motorway trips).
In every diesel BMW I've driven the route on - excluding the 530d - I've not really managed to do much more than slightly better the urban figure. I don't drive them different, I don't thrash them to within an inch of their lives. I just don't tend to get the comedy-high claimed combined figures with them. For reference I've done the trip in 318d, 320d, 118d and 120d. The experience was largely the same with all - I tried extra specially hard with the 118d and just managed to coax a 50mpg average out of it.
By contrast the 530d did 40 and my 530i usually does about 32-33mpg on the same route.
I appreciate this is not scientific but it's a useful thumb in the air.
For this reason I dispute that you'll get 57mpg 'combined' on average use. You might see it long trips, but thats not an average, is it? It's like me saying my 530i does 38mpg everywhere when in reality it does it only on the Motorway and the overall average is noticeably less.
So, I still beleive you'll be further from 57mpg in a 330d than you'd be from 33mpg or whatever it is in a 335i.
I couldn't get 57mpg from an EfficientDynamics 318d on a 200 mile Motorway trip along the same stretch of road at the same speed as I managed 37mpg from a 335i. It did 'about 50'. And that was on a Motorway trip, where the 330d is claimed to do what, 70+?
Housey drives an F10 530d with this same engine in it - he doesnt get 60mpg. He doesn't get 50mpg either, it's more like 40mpg average unless he's on a long trip.
The new 330d is an astonishing package and I'm not sure I wouldnt pick it myself, but you are judging both cars entirely from paper figures which IMHO is grossly unfair.