In engineering theory the 2 stroke can have ca. 40% more power output out of the same displacement. (Not 100% because of significant piston travel needed for the [still quite unperfect!] gas exchange.)
40% more power = 40% more acceleration = 12% more topspeed (at high speeds due to wind drag).
But with emission limits too, the 4 strokes advantage of better gas exchange and cleaner burning become more and more important.
Actual Euro2 50cc scooters of the same low price level have nearly the same power output, regardless 2 or 4 stroke.
The (expensive and error prone!) 2 stroke direct injection is still the best for Euro2 50cc.
It doesn't waste fuel and oil with the bad gas exchange, can have much more power, unrivaled by 4 stroke.
But with much more stringent emission limits of motorcycles/cars the 2 stroke are extinct.
That's the playground for 4 stroke with nearly perfect gas exchange, controlled fuel injection and G-Kat.
