I am the Reds Agent in South Africa and would suggest to rather stick with the GT motor.
The WCS is an great motor for circuit and for sure will not be short on HP for the GT. The gains on the GT will be motor bottom end so you can back off on the clutch to get the car to launch.
Also with Mario Rossi and Team, their motors are designed specifically for their application. Also possible with GT and rubber tyres you wont get the same traction out on circuit foams, hence you could spending more time trying to keep the car on the track then actually racing.
Hope this helps!
RX8 - Savox - Reds Racing - Ko - Contact - Enneti