Originally Posted by Matt :-)

Think of it like this.

Heavier center diff oil would be similar to tightening a slipper clutch. Putting more equal power front and rear.

Thinner center diff oil would be similar to loosening a slipper clutch. Putting more power to the front while on throttle.

The following does hold basic fact / truth, but ultimately comes down to the condition of the track surface and personal driving style.

Heavier rear diff oil may help give you more straight forward bite (as long as the center diff is supplying enough drive to the rear) , but the rear might want to lose traction while on throttle through a turn.

Lighter rear diff oil will provide better on throttle control in turns, and personally I've never really been in a situation where it hurt my speed on the straights.

Hope this is helpful.