There's too many variables to judge the difference in one journey.
Temperature, wind, traffic conditions to name but a few.
For a real indication you need a long term test.
Hi
Ive used v-power before and does seem to make a difference, however not enough of a difference around town to compensate for the extra cost!
Interestingly, Noone seems to have used BP ultimate for a long period yet, people seem to have used V power or Shell Deisel extra more.