How to get even more runtime with a Novarossi engine in my XRAY buggy?

Beside a good tune, 5,5 mm venturi, 9901/41029 pipe set, rather cold plug, prober gearing, clutch setup and a needdle on the trigger..., I thought of the diff's. You'll get better acceleration with thicker diff oil. Otherwise you make a lot of wheelspin and waste fuel, right? Of course you will not have a uncontrolable car, if that's what happens with a change in the diff setup.

Any of you guys tried or thought of that?