[STEFAN V8]

The loss in power is almost totally due to detune of the CPU. You can see in the graph that after 5000rpm the power is climbing less than before. Or on a Natural Aspirated engine the power is going in an almost straight line, with only a slight decrease after the maximum torque rpm. This is also sustained by the value of maximum torque wich is less by 30Nm than in a S/CL/SL, but at the same engine speed

Here is the graph C63 Powertrain Performance Graph for Mercedes-Benz C 63 AMG aut. -08 (336 kW)
and look at the C55 how even it climbs Powertrain Performance Graph for Mercedes-Benz C55 AMG -05 (270 kW)