I dont think there will be much between them - and especially if its going in an old car with knock sensors then there will be minmal performance benefits anyway. I always use the best fuel I can find, but not for tany supposed performance aspects.
Lets face it, fuel is a very low margin business. So, if you invent a super fuel and charge a premium for it, youre onto a winner. The Board and shareholders will love you and drivers of the burgeoning "sport" market are happy. Bingo.