Zelda is more or less unplayable because of layer problems. Super Metroid doesn't start at all. FF3 is extremely slow. All other games I've tried: Castlevania 4, Civilization, Darius Twin, Final Fight 3, Mega Man X, Super Mario Allstars, Super Mario World, SSF2, Sunset Riders and Turtles in Time run pretty well on 133 (unfortunately can't go higher) with frameskip 2.
With optimization, this will become quite nice. Sound and frameskip 2 at 90% speed with 133 MHz would be just fine for me. For now, I'll play the older games that don't use all those effects.