My normal drive to/from work one-way is 40 miles. It breaks down to about 8 city avg (40mph or so avg), 20 freeway (75ish) and 12 (60ish) rural hwy. The OBC reads 21.7 like clockwork.
Long distance open road on the freeway averaging 75-85 its usually about 23-24. That drops to about 21-22 climbing mountains or with a bad headwind.
The same driving in my wife's 03 525i auto is about +5 mpg across the board.