Ive found the best steering setup for me is the HS65mg servo using the Hitec Servo saver kit (esential as the others dont fit) and a DP Delrin drag link. The link needed freeing up a bit to get it smooth but this setup bullit proof.
Ive tried all the different upgrades and none have worked as well as my current setup. I race on a carpet track and the give in the servo saver stops the steeing being too twitchy and makes the car very balanced. The HS65MG fits using the standard servo clamp.