I use Airtronics 94758Z Torque: 115oz/in Speed: 0.06 sec/60 degrees (torque and speed measured at 6 volts) for throttle
and Airtronics 94358Z 200oz/in speed at Speed: 0.10 sec at 60 degree rotation-6 volt operation. I use the above servos in the following cars without any problem yet: Associated T4, B4, GT, and Trinity Reflex On-Road car. I have one JR Ultra Race servo and some Airtronic 94102 servos as backups in case something breaks.
the sx1 thats on my rs4 is ok but when i get it speeding the response isnt very good but it may be that the car goes a bit far and takes time for the radio signals to go and all