The retail fuel companies know what they are doing. Use the highest rating you can find.
The only way that you can now compensate for your static compression ratio is to use a custom cam. It will be leaving the exhausts open for so long, you will be throwing flames out of the exhausts.
Now bear in mind that you need to be talking about actual measured static compression ratio, not "advertised" compression ratio.
Most Ford engines that were advertised as around 10.5:1 actually measure out at closer to 9.5:1.
About the highest static ratio you can run is just under 10:1 with 92-93 pump gas. The ethanol doesn't hurt anything. Don't worry about it.
Sorry to say at actual 10.5 you are going to need the old 103 and it's going to be leaded. That's now Sunoco racing gas and the last time I was on the track was $7.50 a gallon, and left freakin' lead deposits on the plugs that you can't believe.
It also IMMEDIATELY drops your idle rpm down from say 900 with street pump gas to somewhere around 750rpm.
Now the ONLY reason you should even want to run it is for detonation reasons. Higher octane gas produces less heat calories and therefore less horsepower then even regular does.
Don't create a problem that you don't really have.