Well nhra keeps clipping down 1/4 miles to like 1000 feet, and there are lots of 1/8 mile tracks, so maybe the two will meet someday

You could carry more water, but you have to eject it at a faster rate to keep the same acceleration curve (and put more energy into the heating of the water), this may be the optimal size, or there may be diminishing returns worth pursuing. It IS rocket science

wanted to capture some notes from

Waterthunder
"..steam... will reach a velocity of about 1500 feet per second"

"a lightweight tank designed for low pressure will perform as well as a heavy tank designed for high pressure"

"the quantity of water filled in the tank will determine the maximum speed that can be reached"

"The nozzle should first have a converging section then a diverging one, with the exit diameter two to three times the smallest (throat) diameter. The nozzle should diverge at a total cone angle of not over 25 degrees. The convergent section may be rounded to a radius about equal to the throat diameter"