Hi chakota - Either 5th gear or Pulling Power did a test on this last week.
Basically optimax was the best in terms of additional power and low down torque.
But the conclusion the prgram made was that it made no difference on lower powered cars aimed for economy over performance ( if beleived they tested with the new clio diesel ).
If you have a highly tuned car ( such as the scooby they tested ) then you get a much greater increase in power.
Personally ( with the cost of fuel ) I use standard fuel and avoid the lead foot unless I need to use it ( but that's just my middle age family man slant )