Unless the Pathy is loaded, or its very very hot out, I run 87
If it loaded, im towing, or its very very hot out.... i'll top off with 93 and keep using that until it either cools down or the trip is over!
Running higher octane gas, in most cases, will reduce your gas mileage as it is harder to burn than lower octane (and thus resists detonation better under the same conditions)
there are two ways to reduce the chance of detonation in a given engine... higher octane or more fuel (or both)
fuel computers that allow you to lean out your car for better gas mileage take one of those preventative measures away by leaning out your fuel mixture, and, in turn, raising the cylinder head temperature, and therefore, running higher octane is a good idea!
People say, well, my car says to put 87 in the tank, but then why does it better on 93 than it does on 87.
Most of the time its because the engine and fuel system are older and have some kind of fuel / air delivery related problem.
Carbon deposits in the cylinder heads can cause predetonation becasue they hold heat between cycles and ignite the fuel / air charge before the spark plug ignites.
leaks in the intake system can lean out the fuel air mixture by allowing unmetered, and thus, un fueled air into the charge. This is more common than you might think!!!
the fuel injectors also can get clogged or worn, their spray pattern less efficient and put less fuel into the charge (or MORE fuel as well, but that creates a different problem)
The O2 sensors on modern vehicles go a long way to helping with these problems.. but, they don't monitor each cylinder individually, thus the puter gets a "smoothed over" reading on the combustion efficiency and the "problem child" might not get the attention he needs as fuel is corrected over the entire system.
thus, as a vehicle ages, it may require a higher octane gasoline than it was designed for to operate as smoothly as it once did.