Calculations of low free energy structures of gold clusters with a few hundred to a few thousand atoms have been performed. For the study to be computationally feasible, a systematic scheme for generating low energy atomic structures with a given structural motif and a chosen size is used. Comparison of the relative stability of clusters with the decahedral and FCC motifs reveals periodic windows of stability for asymmetric, open-shell FCC clusters while the stability of the decahedral structural motif shows a smoother variation in stability with cluster size. As a result, the FCC structural motif is most stable for clusters with around 440, 610, 800, 1050… atoms, while the decahedral motif is more stable for atomic numbers of around 525, 705, 925, 1175… These new 'magic numbers' represent regions around which a number of asymmetric, open shell clusters of a given motif are most stable, in contrast to the discrete set of highly symmetric magic size structures that are commonly cited. As temperature is raised, the decahedral motif gains stability over the FCC motif. These results help explain reported experimental observations and can guide future laboratory preparations of shape selected clusters.