Question about 3D Rendering with Quadro K2200 + Tesla K80

Both Cards are installed correctly and are detected in Windows and the Render Program.In GPUZ i can see all the Data for GPU Frequenz and Memory Load and all the stuff. If i start with rendering the GPUs from the K80 loads 100% and GPU Frequenz rises up to the max. so far so good…BUT why i can’t see any faster render? Its rendering the same speed if i render only with the K2200
My fault or it is definitely not working?