Any LED you add would reduce the amount of total heat per watt used. More power focused into light instead of heat would help you run higher PPFD if you got efficient fixtures. You might also spend less on cooling and filtering your air. Lots of the new fixtures have remote mountable drivers too, for getting more of the heat away from the plants. Mixing the spectra might have beneficial effect too, HPS is efficient but lacks in blues that a nice full spectrum or UV+IR+White LED fixture would bring to the table.