I use setting two on my back pack. It produces two-litres of water per minute through my pencil jets and is more than adequate.
I'm happy if I can clean the first-floor windows of four semi-detached houses before filling it back up.
I have a few £20 jobs that I can clean with just one fill of the pack. I'm happy with that for the moment and plan to get a small van-mounted system later in the year, or next year; depending on finances, but I bet I will still use the backpack regularly.
When your limited by your water carrying capacity and the time spent replenishing your pure water into your system, a trade-off between water conservation and water pressure needs to be made.
I chewed the fat with Ian_Giles this morning and saw him jetting water out at an alarming rate of knots, but then again, he's got a 650 litre carrying capacity; so he can afford to.