Richie has a page on wikipedia, I know it's not that reliable but it does give some info on his set up.
It has the same thing rumen posted, 10's to play live and 9's in the studio.

Me? doesn't matter what Richie uses I never go above nines, and I like to use 8's on my strat. and the action low, don't know why Richie has the action set so high.