RE: 10C vs 8FG dual rates
You don't program out linkage-caused differential with dual rates. You do that with endpoints.
Page 78 of the 8FGS manual describes dual rates. They apply to Aileron, Elevator, Rudder, Flap, Flap3, Camber, and Butterfly. You don't have rates on every channel. That feature starts with the 12FG.