The advantage of a supercharger is not just peak HP numbers. If you take a standard 5.4 and soup it up to 390HP and then supercharge one to 390HP then the supercharged engine will beat it every time. Supercharged engines, if built properly, have much wider torque curves. The cams have wider lobe centers and the supercharger kicks in right off idle. There is no waiting until the cam decides it wants to let the engine make some power.