I checked a fuel pump today and on it was written PON which apparently is (RON+MON)/2... so it seems like I will have to take my previous comment back... but I will look in to it some more!
If you have 100 octane PON readily availible, you're getting some good fuel. You are right, PON is RON+MON/2. If you're getting 100 RON, it's no better than what we get here.
I got this from wikipedia: "Because of the 8 to 10 point difference noted above, this means that the octane in the United States will be about 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "regular" gasoline in the US and Canada, would be 91-92 in Europe. However most European pumps deliver 95 (RON) as "regular", equivalent to 90-91 US (R+M)/2, and even deliver 98 (RON) or 100 (RON)."