Interfacial velocities during grain growth studies of nanocrystalline materials have been investigated. Two types of interfacial velocity parameters were developed in Ni and Ni-Co alloys. The first was a transformation-averaged parameter based on the time to consume the nanocrystalline matrix by abnormal grain growth. The second was a time-averaged parameter based on the rate of size increase of the largest growing grains. Despite the ultra-high driving force and rapid loss of nanostructure during annealing, the averaged grain boundary velocities are considerably lower than reported velocities during recrystallization in high purity systems for the same homologous temperature. It was found that the time-averaged abnormal growth front velocity decreased with increasing migration distance, which was interpreted in terms of a dynamic sulfur segregation model.