Interesting, I'm under the impression (that could well be wrong!) that the European cars at least are set up to assume 98 RON (hence the sticker on the filler advising not to use less). Using less than the recommended level means that the ECU will retard the ignition to avoid 'pinking' which can damage the engine. So there is no danger to the engine by using lower octane fuel but you will suffer a degradation in performance.

It's a different question as to benefit of higher octane as a more sophisticated setup is required to take advantage this (advanced timing, etc). I would have assumed that that our cars have this but that's a guess. For sure any benefit would be more pronounced in FI engines than NA.