This article presents the results of a comprehensive study of the performance of zirconia-toughened and mixed-alumina ceramic tools in CNC turning of 42CrMo4 steel with hardnesses of 35, 40, and 45 HRC. Empirical models have been developed for the cutting tool lifetime and the surface roughness of the machined surfaces as a function of cutting speed and hardness of the machined material. Through multi-objective compromise optimization via two approaches (the optimal compromise region and the generalized arithmetic mean utility function with weighting coefficients) and the application of a genetic algorithm, the optimal conditions for performing the CNC turning process were determined when using tools made of different mineral ceramics for steel with varying hardness. These conditions provide a tool lifetime exceeding 8 min and a high machined surface quality with a roughness below 1.7 µm.