Managed to get 427.0 miles out of a tankful, which gave me a warm glow. The fillup was only 30.91 litres, so there should have still been 4 litres left, even though the light had been on for ages. This means 450 miles should be achievable. The trip computer said 60.1 mpg for this tankful, and the calculator said 62.8 mpg. 4629 miles on the clock now.