We actually went from Sanwa ERG WRX servo's which are very fast to Futaba 9550's in our TC's due to reduced space for the electrics in our current cars. We've actually found we get on better with these slightly slower servo's, especially in the wet!
We use Hitec 645 MG servo's in our 4WD off road buggies as we wanted more torque than speed adn didn't really want twitchy servos on a bumpy track.