The quasi-steady ELMy H-mode is the preferred operating scenario for ITER. As such, a considerable fraction of the JET experimental programme in general and of the recent deuterium-tritium experiment (DTE1) more specifically has been dedicated to studying the performance and operational limits of ELMy H-modes. In this paper we describe experiments which assess the mass dependence of the performance of ELMy H-modes at the highest currents, fields and input powers currently achievable in JET, as well as of experiments designed to test the maximum density which can be achieved in ELMy H-modes with beam and gas fuelling.