With regard to the trip computer I have a 1.2 ELX 8v and have all the options mentioned. The best MPG I have had was 64.2 but I was going down a long steep hill and did have my foot on the accelerator for most of it! So it probably doesn't count. Usually is about 42-47 mpg under normal driving conditions.
you chould just have a heavy foot like me i used to average about 38 till i got a K&N filter and Eccotek valve now i get about 45mpg. Those figures above are probally granny shifters .