Hi - I had the X1 sDrive20d for 2500 km, as a loaner from the dealership till my 118d gets ready. It had 800km on the clock when I got it, so fairly new engine..
My driving pattern had been 70% highway (ca. 95-100km/h ~ 59-62mph) 15% motorway (ca. 135km/h ~ 84mph) and 15% city.
I reset the board computer when I received the X1, and my total average according to the computer is 5,7L/100 km - ca. 49,58 MPG (Imp)
Unfortunately I didn't note the total amount of diesel I put into the tank - so I don't have the exact number - only the board computer..
(sorry to say but the converter in the link doesn't take decimals into account - so the formula is:
x L/100km -> 282,6/X MPG)