Here is a quote from the link in my post above:
Axle efficiency can be improved by using lower viscosity fluids (such as SAE 75W-90), which minimize frictional churning losses. However, light trucks and SUVs are often used in conditions that expose axles to heavy loads or high operating temperatures. These conditions require superior axle protection, often provided by choosing a heavier viscosity fluid (SAE 75W-140, for example). Commercial vehicle applications may have even more stringent durability requirements. However, providing high durability and long vehicle life often reduces fuel efficiency.
The new viscosity classifications provide more flexibility for OEMs to select the optimum viscosity grade for an application. For example, the SAE 110 grade should be useful in an SUV or light duty truck where improved fuel economy is important but high torque or durability at high speed operation is essential.
Good luck
