The deployment of large electric power supplies in space in the near future allows the use of electric propulsion for transfer missions. The purpose of this paper is to determine optimal mission parameters for these tasks. In this paper, contrary to previous investigations, the dependency of the specific power on the specific impulse has been taken into account. It shows that the optimal exhaust velocities are increased and the corresponding payload fractions decreased. The whole area of a possible optimization is diminished. To obtain a measure for the costs of missions, a transport rate is defined and included in the optimization. It further restricts the optimizable area and increases the specific impulse for higher velocity increments ( Av). For both optimizations, nomographs have been provided to map the whole parameter area of interest for transfer missions. The comparison of different thruster types shows that not only the maximal thrust efficiency but also the form of tjT(c) is highly important for the results.