As has been said, any car engine with knock sensors and an adaptive ECU will benefit from a higher octane fuel. Also, higher octane fuels have better additives which help keep the fuel system clean: this is very important with cars that have throttle body injection.
The fuel info in the AMG suggests 98 Octane. The handbook states that both 95 and 93 Octane may be used, but there will be a loss of performance.
The BMW doesn't seem to care, so it gets 95 Octane and the Morgan gets premium unleaded.
On the old E Coupe, which had a 3.0L Diesel using premium diesel gave a 10% improvement in fuel economy. No idea why.
