Yes i do race mine but here in Finland we do not have a ST class ,so i race with the 1/8 buggies.
i have the RRP diff but i mainly use the plastic diff ,it's mostly a matter of the way you build it and of how much you take care of it,the rebuild has to be done really by the book other wise you will toast the diff all the time .
Locking the diff completely can be done in case of drag racing but on a track you will have really hard time turning in small corners.
When i rebuild mine ,i put 6 spots of AE silicone grease on the outdrives before installing the rings ,then install the rings and balls with just enough AE silicone grease,i also take care of the others ball and rings and install them with AE black grease , then put everything back together ,tighten the main screw and back it of 1/8 of a turn (no more, no less) and then everything should be perfect .
I use in my GT a OS18TZ and i rebuild the diff every 3 months ,so it's not really a matter of power but mainly how you rebuild it that will make the difference .