Well even without the overclock function the game is still freezing randomly... 
I tried with another Wii games like The Simpsons Movie, Wii Sport, Mario Galaxy (but this one is still slow and i can't do anything else without upgrading my CPU) and no one of them are freezing !
I know that my CPU is pretty old but with the newer versions of Dolphin i can "finally" play my favorite Wii/GC games with at least a playable speed
Well thanks for your answer, i wish this problem will be fixed.
I tried with another Wii games like The Simpsons Movie, Wii Sport, Mario Galaxy (but this one is still slow and i can't do anything else without upgrading my CPU) and no one of them are freezing !
I know that my CPU is pretty old but with the newer versions of Dolphin i can "finally" play my favorite Wii/GC games with at least a playable speed
Well thanks for your answer, i wish this problem will be fixed.