Split the difference
I rebuilt my e9 with 10:1 compression pistons. I gambled that higher octane fuels would become the norm, especially considering what appeared to be a swing by some manufacturers to suggested use, e.g., Porsche. I did not bet wisely.
For the most part, I agree with Honolulu. I rebuilt my e9 with 10:1 compression. The engine runs just fine on just about anything put in the tank - unless I decide to push things or if I choose to drive hilly terrain. I have little problem adjusting the ol' Djet manifold pressure sensor, etc. and retarding the timing a bit to avoid the inevitable pinging on full throttle. Unfortunately, this degrades some of the driving pleasure. And, if I use the coupe to commute to work in heavy traffic (which is happening less and less - been rear ended twice), it matters little.
As a compromise, I leave the engine tuned to operate on higher octane and go easy on things. However, when in the mood, I will fill with the higher number or add octane booster (which I keep in the trunk). I have the same issue with a Pontiac 455 S.D. engine, which, unfortunately, is even more demanding or less understanding than the e9. As much as I enjoy the pleasure of driving both cars, circumstances are making it not as easy as it once was. Aside from adding octane booster or filling up with higher octane fuels, there is another possibility - water injection. My former neighbor did this with several of his vehicles. He had the advantage of having worked on piston driven aircraft, which is what motivated him. As I recall, kits were available for carburetted engines from J.C. Whitney, although I have no personal experience.
Another neighbor pointed out that his newest Honda runs 10.5/1 compression on regular grade fuel. While I am not familiar with the setup or whether a knock sensor is employed, the general literature suggests the variable valve timing is the accommodating feature.
