In this paper, design space for variable flux (VF) machines is examined in a permanent magnet synchronous machine (PMSM) parameter plane based on constant parameter, lossless power conversion properties, and estimated total loss distributions (i.e. copper and iron losses) while applying a d-axis current constraint based on an assumed demagnetization characteristic. Medium-to-high speed, partial torque operation is typical for duty cycle loads, such as in the case of the electric vehicle. VF machines can reduce losses in these operating conditions by reducing the internal magnetization state of the magnet, thereby reducing flux linkage associated with flux produced by the magnet. In this paper, VF machines with large normalized permanent magnet flux linkage which are in the highly salient, flux intensified (FI) machine design space (VFI-IPMs) are shown to have large maximum torque, rated power, inverter utilization, and constant power speed ratio (CPSR) as well as low losses in the low torque region over a wide speed range when compared to conventional fixed magnet flux PMSMs.