A methodology based on FEM-calculations and experimental tests for predicting coated tool efficiency in milling Ti6Al4V by coated cemented carbide inserts is introduced. The used coatings were: (Ti,Al,Si)N and (Ti,Al)N films. The stress-strain curves and the fatigue critical loads of the coatings were determined by nanoindentations and impact tests respectively at various temperatures, employing FEM-supported procedures developed for results evaluation. The milling investigations were conducted at various cutting speeds. The stress and temperature fields in the cutting edge region were obtained by FEM calculations of the milling process. These results facilitated the explanation of the coated inserts’ cutting performance versus the cutting speed. The cutting tests at various cutting speeds and the impact tests at ambient and elevated temperatures revealed that the tool life and the film impact resistance versus the temperature are not linear. Moreover, a sufficient correlation of the coatings’ impact resistance at various temperatures with their cutting performance at corresponding cutting speeds was revealed. In this way, an adaption of the cutting conditions to the films’ temperature-dependent strength can lead to a considerable cutting performance improvement.