I discovered quite a number of videos on youtube demonstrating the effectiveness of over-clocking the CPU of Sega Genesis/MasterDrive. The video features games that are known for their intensive rendering procedures such as Flash Back, Pebble Beach Golf and Hard Drivin'. As one might have guessed, the games ran at a much higher fps rate and looked smoother. It also appears that the actual modification of the console is surprisingly simple, involving connecting the clock pin of the 68000 to new crystal.
This naturally made me wonder how such behavior was possible. It is known that many older 8bit computers such as the C64 where unable to support over clocking since the CPU clock was also tied to the video clock. Any changing of video clock would result in unstable video output. For over clocking to be useful, a system that supports chips with different clocking rates would be needed. Hence, only game logic would be speed up and not core system I/O interface. The Genesis does in fact satisfy this precondition.
Doing a quick search for over clocking on SNES results in a limited success. I can only find examples with the SuperFX chip. At the hardware level, why has the SNES seen so little success in over clocking of games?