Originally Posted by Roelof

In the early days we were running analog 4kg with platic gear servo's. Today's onroad cars and buggy's are fine with 8 to 10 kg servo's with a speed of 0.07 to 0.1 sec over 60 degrees turn.

I must say I changed the servo in my 1/18 car from a speed of 0.11 sec to 0.05 sec version and on our tight indoor track it was much easier to take the tight corners. So yes, when you have a short track with fast left-right corners some speed is helpfull to to take the corners more precise.

By the way when you are running a normal non high speed transmitter (like an old DX3) you first should make a step to a transmitter with a high speed framerate and low latency. this can speed up your reaction time up to 25msec without needing a faster servo.

For throttle I sugest to get a same servo as for the steer so you can buy a 3rd as spare for both positions.

Last week I was at a shop that was quiting their RC department and I could buy some Spektrum H6205HV servo's with 50% discount, Funny thing is that the servo cable is connected by a 3-pin connector to the servo, that is nice for a faster servo replacement. No rewire needed.