I'm not real sure... I just did a quick search on the CDFreaks forum and the only reference to it I found was where some guy said a few years ago he OC'ed his Ricoh 4x to a 6x...
I think if you want to try to overclock it, you may be the Ricoh guinea pig! :)

guinea pig?

i thought, way back when, they overclocked by changing jumpers, rather than firmware upgrades. also, i believe any drive using a mediatek chipset can be overclocked :D. duno about others, though. mtkflash makes the job much easier.

oh yes..it does....