Optimax is good if you get through it quickly. It has a tank life and degrades very quickly once reached! It is refined at 98.6 RON (not MON) and degrades after around 40 days. I wont bore you with the deep down technical details, but it does!
In this 40 days it has to go from the refinery into the tanker, and then be transported to where-ever its going, possibly stopping over-night many times on the way.
So it has arrived at the forecourt now. Shell always put it in the smallest tank available as they are aware of the degrading. Now an average Optimax tank is 10,000 litres. This means that if this fuel is not sold quickly it WILL degrade. Even if you get some from the forecourt before its 40-day shelf-life you still have to use it all within the 40-days as well.
RobFenn: There is no way Optimax can improve your top speed. No way in the world.