1.4x4 pistons is similar to 1.6x3. Given that piston hole size and comparing some of setup from the pro drivers, they are using somewhere around 450 in the front and 400 in the rear. 300 is way too light for carpet.
Why do you run so soft in the front on carpet? The car will end up having tons of LOW speed steering when you are off throttle, and the front will lift giving you no steering anytime you touch the throttle.
Whereas if you are using 1.2x4 pistons, then the oil range is somewhat close.
Why don't you start with Craig or Hupos setup and go from there?
http://www.petitrc.com/setup/durango..._GenericSetup/
http://www.petitrc.com/setup/durango/setupdex210/DEX210_HubertHonigl_Dortmund2013041314/