That depends on what comes out of the faucet. We recommend a temperature setting of 130. Much higher and scalding occurs very rapidly. Much lower and legionella bacteria can grow in water heaters. But residential tanks can vary a lot in how hot the water is they produce. Best to test with a meat or candy thermometer at the tap.
But the real question is, why do you think you need a new water heater? Maybe you just need a new dip tube or some other component. Why don’t you tell us more about why you want to crank up the thermostat to max.