I was running 18 or 19 -104 with a brussed 10 turn Reedy motor at Eden Park.
Just check the heat on the motor after your run. to be honest I didn't notice much of a difference from one tooth.
I'm making the jump to a 10.5 brushless this weekend though just to slow myself down.
My plan for the regional is to keep it on 4 weels and learn to drive again.
