Higher octane will actually net you less horsepower...however, if the computer can sense the octane and in turn, retunes the truck on the fly...you will notice a difference, but, the Hemis will only do that for 89...running 93 is just a waste of money for no gain.
A big misconception is that higher octane fuel makes more power...but, really, all the octane rating means is, the higher the number, the harder it is for it to ignite.
Basically, you want to run the lowest octane you can without engine knock "ping" (pre-ignition/detonation). Lower octane fuels have a lower flash point, therefore can preignite more easily. By running a higher octane, the fuel is actually igniting later in the engine stroke.
The reason high performance vehicles usually call for higher octane fuel is because they have a more aggressive timing curve which makes them more prone to pre-ignition. Also, boosted vehicles need it since the air charge is so much hotter than on an N/A engine, it can cause pre-ignition simply because of the heat...same with high compression n/a motors. Pressure goes up, temperature goes up, chances for knock go up.
So, run 87 if you have a 5.2/5.9L, and, if you have a hemi that recommends 89, you'll get the best performance with 89. Unless you have a 93 octane tune, our trucks don't need 93 octane. If it pings, step it up a grade, if it still pings, you have an issue that should be fixed. (either running lean, too much slop in the timing chain, or oil is being introduced into the combustion chamber).
Also...oil has a very low flash point making it ignite very easily...thats why if you have a bad plenum gasket in the magnum motors, they ping so badly.
Just some random facts I figured I'd enlighten this thread with so people don't go wasting money for no reason