Highest Octane For Stock ECU??

USNA94

Here in the states we post the average of the RON and the MON. Other countries sometimes only post the higher number.
The below explanation is copied from: How Much Octane Do I Need?

What is octane? How can it help my engine? two laboratory octane numbers determine the overall octane quality of a gasoline. Both numbers are determined in single-cylinder, variable-compression-ratio engines. The first is the research octane number (RON), where operating conditions are mild. This is the number that gas stations in the 1960s put on their advertising signs out in front, numbers that ranged from a little over 100 to as high as 104. If an engine is detonating (pinging) at part throttle, it usually needs more RON.

The second laboratory octane number is also determined in a single-cylinder, variable-compression-ratio engine and is called motor octane number (MON). The MON test is conducted under more severe operating conditions (higher rpm and higher inlet temperature) than the RON test, and as a result, the number is lower. If an engine is detonating at wide-open throttle, a higher MON will usually satisfy it.

The number shown on the black and yellow sticker on the service station gas pump is the average of the RON and MON, or antiknock index (AKI). If the sticker shows an AKI of 92, RON is typically between 96 and 97, and MON is typically between 87 and 88. The RON and MON can vary slightly but still must average a minimum of 92 to have a pump posting of 92. Higher octane unleaded fuels will have a greater difference between RON and MON. For instance, 76 Unleaded Racing Gasoline has a RON of 106 to 107 and a MON of 94 to 95, which gives an AKI of 100 to 102.