is there a problem with Cybervision 64 at over clocked a3640 to 30mhz or dumb to worry about everything is okay with GFX ?
It will work without problems. It would be a good idea to add a small fan to the 040 if you overclock it.
BTW, keep in mind a 040/25 loads images (e.g. jpg) quite faster than 030/50.