Accurate geoids are expected to improve our knowledge of the dynamic sea surface height (SSH) as a mirror of the dynamic state of the oceans. The dedicated Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) mission will lead to a highly accurate geoid model with a resolution of degree and order 200. We examine the impact of this mission on the assessment of large-scale oceanic mass and heat transports via its expected error characteristics. We do so applying a linear box inverse model and a nonlinear section inverse model to hydrographic data and to (synthetic) SSH data. The results are compared to those obtained when substituting the error estimates of the Gravity Recovery and Climate Experiment (GRACE) mission and the present-day Earth Gravitational Model 1996. For the box inverse model we find an average reduction in transport uncertainties of about 9% for GRACE geoid error covariances and about 17% for GOCE over the hydrography-only solution. In both GRACE and GOCE these average percentage improvements are significantly increased when model error is excluded. Summarizing our results and those of the companion parts of this study, we conclude that the GRACE mission reduces the marine geoid uncertainties such that altimetry may become useful for the study of the steady state ocean circulation. The GOCE mission will improve the accuracy of the circulation estimates significantly on the large scales and introduce higher accuracy on shorter wavelengths as well. Furthermore, it will enable us to study individual ocean currents.