The above is correct. Buy out west 87 octane is premium. But Ford says to stick with 87 so you'll be pumping premium rather than regular. You need to pay attention to the labels on the pump when at higher elevations.
Higher octane only benefits higher compression engines. In the V10 it will usually result in fewer MPG unless the Premium grade is Ethanol Free. To many the Ethanol content will be a bigger concern than the octane.
__________________
Neil V
2001 Winnebago Adventurer WFG35U