I drive mine every day. Mostly motorway miles.

Example of the fuel economy as follows.

Warm up, no more than 2500 rpm till 75 degrees on oil temp, motorway run, fast, around 120-130 whenever possible (lots of it), runs to limiter maybe 3 to 4 times a tank. A little bit of traffic movement due to getting in and out of Edinburgh. It invariably returns 24mpgs

If you cruise at 70 on motorway, u get 30-35mpgs.

Edited to say - to get as low as 20mpg u must be roasting it around towns, or u must be sustaining more than a constant 130mph. |I have seen 18mpg on cruise control as per porkies comments. That is usually around 140+ on cruise

Cheers

RW