All versions of the 5.0 liter direct injected engine recommend 91 octane (North America) with octane as low as 87 fully acceptable with possible performance loss. The engine management computer with this motor is more sophisticated than with the old 4.2, allowing lower octane to be used with no fear of damage.

All that being said, what is the point of compromised performance in such an automobile? There has never been anything less than 91 in mine, and nearly always I burn 92, the highest available in my area.