Octane = Residence to burn
The higher the octane the longer the molecule chain. Which in turn means to things.
1) It's harder to burn (takes more heat to combust)
2) you will get more "power" out of it, because there is more of a molecule to break down.
So, an engine is designed to run at a certain temp and compression ratio. This translates to what octane level fuel you should use.
In a high performance engine "high temp and high compression ratio" you need a fuel that will only ignite when the spark goes off. Not ignite because of high temp before the spark. (Thats why you get poor performance when you use 87 octane in an engine that was designed for 92, the fuel keep burning before the spark)
Now, the other way..... The fuel could "potentially" burn after the spark or take to long because the temp and compression was to low. But, I think this is less likely that the other way around.
So, unless you have a problem ... I think you should use the octane that was designed for the engine.
My 2 cents