You could've read the plugs to see if they were fouled or had metal on the white part meaning detonation. At this point, I'd get a cylinder compression check done to make sure there wasn't any permanent damage done.
That stuttering you were getting at the top with the 91 octane was likely knock/detonation.
Running a lower octane will cause your car to adjust its fuel trims richer. When you replace the low octane fuel with the higher octane 93 it's going to take the car a little time to readjust its fuel trims back to normal; during that time, you'll run a little rich.