Here is what you do. If you have a gauge between the pump and the unloader, turn the pressure down to about 2500psi (I have seen some of these 13hp 5.5gpm machines make around 2500psi) and put the 0040 or 0050 nozzle on your gun and pull the trigger and see how far it shoots. Mark that spot with a cone/brick/employee, whatever.
Next put the pressure back to where it should be and spray beside where you sprayed before and mark the spot and see how far apart they are, might not be more than 10' or so with the pressure difference.
If you are using this for house washing, you will probably be using the fan mostly except for the soffits and eaves. This rig should be able to hit the soffits and eaves of most 2 story houses. If it does not spray that high then you need a bigger engine for that pump. The gpm and psi is what gives it distance.
Like in my example earlier with the 5.6 and 8gpm machines, the 8gpm will shoot higher and further than the 5.6gpm machine. I can hit the soffits and eaves of a 3 story building with either machine but on a windy day I will use the 8gpm machine as the wind will not affect the spray as much as the 5.6 machine.