What is the correct speed of the PAL Master System games?

[retrojatekos]

I use Fusion emulator. I try to play the Wonder Boy in Monster World game, and I saw, that this is an Euroe-only release. In default, the emulator works as an US machine, at 60 Hz. I switched it to Europe, and the game become slower. I know, the PAL frequency is only 50 Hz. But which is the real speed of this game?
In 60 Hz:

In 50 Hz:

[flatapex]

correct speed is 50hz, some prefer to play at 60hz, on some games this makes them VERY difficult I would have thought