Just did some 'controlled' testing on a long run today. Overall average sits around high 27's / low 28s mpg.
Constant 50 mph, motorway, cruise control in - 38.5mpg!
Constant 70 mph, motorway, cruise control in - 34.6mpg
Varying between 50-80mph, motorway, cruise in, gentle acceleration only - 33.2mpg.
All taken as averages over a 20 mile stretch each.
I guess my engine is in pretty good shape then!
(figures as displayed on dash, so prob a little optimistic?)