Production optical proximity correction (OPC) tools employ compact optical models in order to accurately predict complicated optical lithography systems with good theoretical accuracy. Theoretical accuracy is not the same as usable prediction accuracy in a real lithographic imaging system. Real lithographic systems have deviations from ideal behavior in the process, illumination, projection and mechanical systems as well as in metrology. The deviations from the ideal are small but non-negligible. For this study we use realistic process variations and scanner values to perform a detailed study of useful OPC model accuracy vs. the variation from ideal behavior and vs. theoretical OPC accuracy. The study is performed for different 32nm lithographic processes. The results clearly show that incorporating realistic process, metrology and imaging tool signatures is significantly more important to predictive accuracy than small improvements in theoretical accuracy.