Dolphin, the GameCube and Wii emulator - Forums

To summarize: not all games require the same specifications to play and thus not all games will you at the same framerate with the same configuration, new super mario bros wii belongs to the "lightweight games" family, meaning it isn't very demanding and will require much cpu and gpu power than a game from the heavyweight family such as super mario galaxy 1 and 2, xenoblade chronicles, monster hunter tri, twilight princess, etc will need, this is why you get such a good performance on it compared to other games.

Turn that OC back on, especially if you already have the cooling. It might be enough for your PC games, but it's not for Metroid Prime. Then when you're done, revert the OC profile and re-enable dynamic frequency scaling so it'll ramp up during workload and idle cool the rest of the time.