V power is better than standard 95 ron. I use it as much as possible both in by clio and VTR. You can use sainsbury or tesco high oct. fuel too it doesnt need to be V-power or BP ultimate. If expense is an issue you can by some stuf from halfords that cleans deposites from your engine, however if you drive it hard every once in a while that will do the same thing.
you should always get more MPH with V power over 95 ron normal fuel.
To test how effective Vpower is over normal fuel you must do the same journey at the same speeds and at the same acceleration rates!! If Vpower comes up short of milage over normal ron fuel these factors are more than likly to have changed, remember milage doesnt take into account hills.... heavy feet.... or harsh braking....