Static compression has little to do with the octane needs of an engine. Cylinder pressure is the main indicator. A simple cranking compression which can be estimated on a lot of engine design software will give you the best indicator. Just from my experience for 93 octane you want to keep the cranking compression in the neighborhood of 140 to150 psi. I use performance trends software but a lot of them out there. Performance Trends actually calculates the cranking pressure and generates an advance curve to use whatever octane fuel you select. I find it pretty accurate, when running an engine on a real dyno that I set up with the software usually the max HP timing is within a couple degrees of the prediction. And HP predictions are always within 10% And also it is not so much how much compression you can run but how much timing you let the engine have as well. 91 octane to E85 is not an apples to apples comparison for a fuel type in regards to detonation. Just to see I pulled up an old engine build and between 91 octane and E85 the computer took out 10 degrees of timing for the gasoline. And it made 50 HP more with the E85