I managed to get 59 from mine once on a motorway trip.. 1.4 16v. I have never been close since. I don't know if the computer is crazy
you need to do a bit more than 70 miles before you get too excited, and an average speed of 44mph means most of it was at fairly high speeds. if I drive from here to london and reset the dash once on the dual carriage way then most people could easily match those figures
do 300 miles in and out of town and you'd not get anything near that