75mpg.... that might be the e90 320d mate??
I cant see the E46 330d putting that out at light cruise, even after mapping has optomised the consumption. It'd do 45-50mpg tops on a very light cruise.
If its getting a genuine 60mpg+ on motorway duty then I'll book my old dears E46 330d Cabrio in because she's getting 36-37mpg at present.
Cheers,
Grant