I swear by BP ultimate in my valver (when i can afford to put some in, poverish stoodent you see
). The car pulls a lot smoother low down in the revs and i do notice a difference in consumption. A lot of people will say is all in your head but in my opinion its not.
A high octane fuel has less tendancy to predetonate which will be why people think it makes the car pull smoother. Also high octane fuels have a much mroe controlled burn, allowing the flame front to spread better throughout the combustion chamber. the better the burn the rate of pressure rise and hence the more power can be harnessed from the process.
It is not true though, that higher octane means more power within the fuel as a litre of deisel contains more energy than a litre of petrol yet it has a lower octane rating.
The basic idea is yeah, its well worth using higher octane fuels if you can afford it. Cant do any harm can it!
Hope this helps
Shorty