You need to see which method your Euro Octane rating method is based on. There are/were two methods that were used in the US; Reasearch and Motor methods and each used a different scale to arrive at the octane ratings. I no longer have that information in my brain; however.
If you look at US gas pumps and the Octane rating, you will see the number as derived from the formula R+M/2 which is the average of the two methods. I do remember that one of the methods was based on 100 being the highest octane number while the other could go higher (i.e., 110 Avgas, etc).
Perhaps someone else on the list with "recallable knowledge" on this might help. I do know that I run 93 octane in my 71 250C and it does very well - no ping or knock and the plugs are not damaged. Works well even when the ambient temp is in the 105+ range.
Dan Taylor/ Tulsa, OK MBCA '71 250C/'81 300TD-T