't be any
Department of Health, here recomend at least 160 deg F for safe and sanitary dish washing.
However if small children are using taps that may be too high y to avaoid scalding.
On the subjcet of efficiency; it depends where the 'wasted' heat from an older less well insulated tank will go. In our case it escapes into and helps heat the house which requires some heating for at least ten months of the year and is heated electrically (from hydro generated power) in any case.