Hi,
I don't claim to be a real expert but this works for me with a TC3 on road. If you are racing it depends on the race time. If you run too high gearing 1, your cells won't last the time & 2, your motor/esc will get very hot!!! So find a balance between speed, runtime and motor heating up. I usually keep going higher in practice until the motor gets too hot to touch then come down 1 or 2 teeth.
Hope this is some help!!