[rotrex]

Once you are able to hit MBT ignition timing for a given boost level, more water to fuel won’t gain you more power.
it will continue to slow down combustion speed requiring more and more ignition advance for no power gains.

Jut make sure lot’s of the spray actually making it into the combustion chamber. Spray does not like to take any bends. Poor nozzle location and intake designs unsuitable for wet flow tend to puddle the water letting it pass as big drops straight though the engine into the exhaust.

if you let too much of the water evaporate within the TC, you might gain some total density, but you hardly gain a higher oxygen partial pressure due to vapor dilution. The main effect of the water is not due to IAT reduction, but from suppressing temperature peaks within the cylinder, specifically near the walls. It needs to be present as tiny droplets to do this and not as a vapor.

Some metal bits in the engine benefit from some cooling admittedly.

Are you knock limited at all?