Unhappily, the accident record bears out this articles main point: Combining STCs and performing untested modifications can have lethal effects.
August 7, 2010, Saltsburg, Pa., Beechcraft Model 58 Baron
The accident aircraft was modified by one STC that installed vortex generators (VGs) and by another for more powerful engines, different propellers, winglets and modified engine cowlings, which also increased the airplanes VMCA. However, the airplanes airspeed indicator remained marked to indicate a lower VMCA.
