What SEGA GENESIS/SEGA CD game had the most slowdown during gameplay?

My overclocked JVC X'EYE is almost done. When it arrives, I would like to show a friend the difference between a SEGA genesis game with slowdown, and the same game with the overclock setting on.

I know Sonic the Hedgehog 2 is a prime example with it's 2 player mode essentially running the same game twice, but what are some other games I would notice a large performance difference in?