I know EXACTLY what you mean, Devolution makes multiplayer "single race" in Rush 2049 on "Midway Arcade Treasures 3" actually be playable - on the GameCube 2 players has random hiccups which just gets annoying and 3 players just runs at like half speed the entire time. In Devolution 2 players is darned near FLAWLESS while 3 players runs at actual playable speeds.
Either way, that improved framerate "patch/fix" is actually just a side effect of how Devolution works since AFAIK it just patches the necessary GameCube code to run with Wii equivalents, much like WINE on Linux does. It's my understanding that it's not much different from the official GameCube to Wii ports that were made of various games, if in fact any different at all. In fact before Devolution was released tueidj himself stated that he didn't think this "feature" of running at full Wii speeds would make a noticeable difference in game performance.