Synchronous reluctance machines are becoming a widespread solution in many engineering areas thanks to their simple rotor structure, the absence of rare-earth permanent magnets and high efficiency. The design of such machines is a widely investigated research topic, given the challenge of analytically estimating their electromagnetic performance, especially when a high-speed scenario is considered. The design choices and assumptions, which include the selection of the magnetic load and the stator and rotor lamination materials, play an important role in the machine performance. Consequently, it is of paramount importance to assess their validity. This paper, after a brief re-call of a general design methodology able to consider all the magnetic non-linearities and structural and thermal limitations occurring at high-speed, presents a sensitivity analysis against the magnetic load when a Cobalt-based alloy is adopted for both stator and rotor laminations. The analysis is carried out for different speeds up to 90 krpm, in order to draw general design guidelines for a given outer envelope and cooling system.