I drove thru all of scandinavia recently, and there were only two grades of gasoline available there - regular and premium. Regular was 95 octane ((R+M)/2), premium was 98. All cars use one of these two.
So why are we cribbing/discussing using 93 octane in the US? It's lower than regular in a lot of countries (cost aside).
FWIW, as compression ratios are going up and tolerances down, the octane requirement in fuels has been steadily going up. Heck, 30 years ago, 83 octane was used very commonly. Why don't we discuss going back to 83 now? Another 10 years, and we'll accept 93 as "regular" and go on with life.