There's not a one size fits all when it comes to knowing what combination of timing, compression can be run with what octane fuel. MANY, MANY variables are involved - combustion chamber design, use of the vehicle, ambient weather conditions, age/condition of the engine, head material, cooling system condition -- the list goes on and on.
There's no benefit to running any higher octane than you have to in order to support your set of variables. Most stock-headed 5.0's can get by with 12-14 degree timing and still run 87 without detonation. But if yours won't either up the octane, or cut back on the timing. What someone else's does may or may not be duplicated by yours. I have aluminum heads on mine - stock bottom end and mild cam; it runs with 16 initial timing, 32 degrees total in by 2800 rpm, and it runs on 87 octane without a hint of detonation. And, it seems to get about 1 mpg better mileage (city and highway) on 87 than on 93. Probably because the 87 octane fuel is ignited more easily and burns a bit more quickly than the 93. For cars with lots of timing and/or compression, the benefits of running the higher octane to avoid detonation outweigh the slower burning characteristics of the fuel.
I get 300 miles/tank on my stock setup here.
