This paper presents a methodology for the sizing and synthesis of power generation and distribution (PG&D) subsystems. The PG&D subsystem models developed in a previous work done by the authors were applied within a parallel hybrid electric propulsion architecture using the Dornier 328 as the baseline aircraft. The hybridization took place only during the cruise segment. Analyses were performed in Pacelab SysArc, a system architecture design tool, to assess the impact of different hybrid electric propulsion architectures and changing PG&D subsystem characteristics at aircraft and mission levels. To this end, sensitivity analysis was conducted to reveal the sensitivity to the subsystem level characteristics. Moreover, six different architectures were compared in terms of their mission level performance. These architectures included the PG&D subsystems with current state of the art technology, NASA 15-year technology goals and a more advanced battery technology. Although neither the current state of the art PG&D subsystems nor NASA 15-year technology goals were advanced enough to match the design range requirement of the baseline aircraft, some of the competing architectures met the practical range target while enjoying substantial amount of fuel reductions. Finally, it was observed that in order to reach a break-even point in terms of the design mission range, a battery specific energy of 5 kWh/kg was necessary for a 50% level of hybridization during cruise. In this work the Dornier 328 was used as a testbed, however the methodology can be generalized for all parallel hybrid electric propulsion applications.