This paper presents a parametric study on the stability and control performance of proportional velocity feedback control with square piezoceramic patch actuators of various widths and thicknesses, used to suppress the vibration of a thin rectangular plate. A simple stability-performance formula has been derived, which, using the open loop sensor-actuator frequency response function, gives the maximum control performance that can be produced by such a feedback loop at resonance frequencies of the lower order modes of the plate. The parametric study has been carried out using simulated sensor-actuator frequency response functions. The results have been validated using measured frequency response functions on sets of rectangular panels with a square piezoceramic patch of various widths and thicknesses. The parametric study has shown that the control performance is significantly improved by increasing the width and reducing the thickness of the square actuator.