I travelled from near Worthing to Brussels and back in a day many years ago on a single tank of fuel....
The trip was literally for a 15 minute meeting, and just for a laugh I did a 'Clarkson'. Air con off, radio off, 55 mph on the way there etc to see just how many miles the old girl would do on a tank. From memory, the journey was circa 600 there and back and the car started coughing about a mile from the station I'd filled up in earlier that day. When you consider towards the end of our relationship I was only getting 250 miles or so to a tank I was quiet chuffed.
Great cars and I loved the V8
Best journey though was from just by Monaco to Worthing (about 900 miles), overnight in a single hit when I had the 3.0D Sport X5. Got out of the car at home mid afternoon and felt like I'd just stepped into the car - absolutely made for the journey.