Prospective exascale systems and large-scale cloud infrastructures are composed of dozens of thousands of nodes. Evaluating applications that target such environments is extremely difficult. In this paper, we present an extension of the Distem emulator to allow experimenting on very large scale emulated platforms thanks to the use of a VXLAN overlay network. We demonstrate that Distem is capable of emulating 40,000 virtual nodes on 168 physical nodes, and use the resulting emulated environment to compare two efficient parallel command runners: TakTuk and ClusterShell.