You are correct that you can turn it down, but in doing so, you DECREASE the gpm (flow), and therefore, the cleaning power of your washer. The nozzle creates the pressure, the pump pumps a set amount fo fluid, the engine drives a the pump at a speed. The law of nozzles requires a fixed amount of fluid for a specific pressure. For example, an '04 nozzle performs as follows: 1 gpm at 250 psi, 2 gpm at 1000 psi, and 4 gpm at 4000 psi. None of these are a good choice for what you want to clean. If you really want to clean something, then I recommend a washer that has the ratio of gpm to psi of 1:350. This is roughly what self serve car washes have. They operate at 3.5 to 4 gpm and 1000-1200 psi. If you want to spend a lot of money and have a very limited use (useless?) washer, then buy a 4 at 4000. If you want to have something that will clean very well, then increase your gpm and lower your pressure. The practical limit for flow is about 5 gpm, since most garden hoses cannot keep up. A 5 at 2000 or 2500 psi would a wiser choice IMO. If you still want the 4 at 4000, then use a dual lance with either an '05 (2500 psi) or an '06 (1800 psi) in the other side. You will probably like the cleaning ability so much that you will wonder why did I spend extra for '4000'.