Running the Stealth Muscle cover and it does help with engine reaction time. This engine, with its torque and short rpm range reminds me of a diesel engine which is a massive air pump. You can hear the noise of the air intake. I also understand that the original hockey puck of a cover was modeled to help damp out engine noise to conform to various countries noise laws. It does not help performance.
As Richard Wood stated there is not much point going above 5200rpm. Even there the engine is ragged. I keep mine between 3000 and 4700 rpm. I find the tach to be very accurate compared to the fuel gauge.
