Not an electric guy yet, still haven't converted anything but as its been said. Your diff fluid choices depend on your driving style and how you want the car to react to throttle input.

I run a modded Novarossi 528xr that is pretty much a monster. The powerband is very linear from about 10,000rpm to 30,000rpm. Tops about 60mph with a 16t clutchbell.

I'm running 10/100/3. Yes, 100k in the center diff, not a typo.

This truck is going brushless first, but I probably won't run lipos. I'm a little crazy and would send it 40ft into the air without a 2nd thought.