An often-overlooked aspect during the development process of electrical machines is the validity and accuracy of the machine material properties being used at the design stage. Designers usually consider the data provided by the material supplier, which are measured on material in an unprocessed state. However, the fact that the machining processes required to produce the finished product (e.g., the stator core) can permanently vary the material properties is very often neglected. This paper, therefore, deals with and investigates the effects that such processes can have on the overall machine performance. To do this, three sets of material data, the material suppliers' data, material data based on conventional characterization methods, and material data based on test samples that include the manufacturing processes, are used to develop three versions of the same baseline machine. The results of these three machines are then compared, and the resulting variations of the machine's performance are presented and described. The chosen baseline machine is a high-performance and relatively high speed, aerospace, electrical machine. Special attention is focused on the efficiency maps of the machine, as this aspect is highly dependent on the material properties that are the mast sensitive to manufacturing processes such as the material's anhysteretic B-H curve and its specific core loss.