I use a Hitec 525 in my gas truck for throttle. it has 57 0z of torque with .13 speed. I have also used a jr 590. thats about 85 oz of torque and .15 speed. They are both metal geared servos. And theyre both around 40 bucks. The hitec is a little faster but dosnt have as much torque as the jr. I like it to be a little bit faster because you dont need that much torque to stop a 2wd nitro.
soI think 50-100 oz of torque and anything faster than .15 seconds would do a more than suitable job.