I use my D24T engined 740 for mostly long journeys.
It's stock (with M46 gearbox), except for an electric cooling fan. I typically don't exceed speed limits, but don't sit below them either. It's normally only lightly loaded.
Mine has averaged 46 UK MPG (equivalent to 38.5MPG US) over the last 4000 miles, and approx 44.5MPG UK (37MPG US) over the last 15,000 miles.
Pretty happy with that
