What other differences does a different size pump make?
The more horsepower that makes it to the nozzle, the faster you can cut. The trade-off with a higher horsepower pump is cost, effeciency, a larger kerf width, and sometimes a slight loss in precision. However, a high horsepower pump can almost always be run at lower pressures to reduce the operating cost and maintenance, and then run at higher pressures for special jobs that would otherwise try your patience.
