I ran an F30 320ED for 35,000 miles and regularly acchied over 60mpg, average was 58mpg and worst I ever achieved eas 50mpg.
This was mpg calculated by fuel in and the odometer too.Typically this was on the region of 10% less than the computer.
I now have a Merc A200 CDI and that averages 52 mpg under the same driving conditions and is less powerful too.
I was always impressed by the economy ,more so that it never felt short changed for power.