I have a Clio 182 and my girlfriends got me a driving experience in an Aston Martin and a Lambo, it's just past Birmingham 180 miles each way has anyone ever had 360 miles to one tank?
Going motorway speeds takes the revs quite high on a f4r. If you drop speed to keep the revs lower you get a large increase in mpg, more than you would see on another car without the high revs.
For example, my avensis sits a good 1500 revs lower than the clio. Dropping speed in the avensis does not save as much fuel as dropping the same speed in the clio. You only have to do 10-15mph less to see a large increase in mpg.