Originally Posted by Xan

For non premium required vehicles that's true if you get a incomplete burn.

However if it does burn, premium fuels burn cleaner then non premium.

I don't know the Nissan ECU (but will be putting some time into this in the future), but for Jaguar's ECU's the advance timing map went well above the minimum octane spec in advancing timing under heavy load and has build in algorithms that take care of the ignition learning. So assuming that Nissan (or who makes their ECU's) do a similar thing, it actually would make a difference to use higher octane fuels.