I doubt even mapping will have much of an impact, the biggest difference is the Haldex drive train.
I've found that deducting 5 mpg of the Official combined figure usually gives a realistic day to day MPG.
The type of driving will influence this too...rarely saw much more than 29-31 mpg with the MK5 on 10 mins of A road stop/start driving combined with 20 mins of Dual carriageway.
Now in the MK6 most of the journey is uninterrupted 50-60 mph and I frequently see 40 mpg....until joining carriageway
.