There is race fuels and there is race fuels, lots of crappy fuels on the market with flashy stickers and websites...
9 times out of 10, go with the fuel the engine-modders recommend, they see a lot more and try a lot more then most others.

Supertib is correct, a to high-grade fuel will prolong the break-in and put unnecessary load on conrod etc.
Plus that it will give a "false" break-in, meaning the surface of the piston has more or less been deformed to match instead of lapped to match.