Hi chanster00,
Its not the simplest answer in the world as there are a number of factors that must be taking into consideration.
1/. Having the correct flow rate can indeed speed your working method up. If you had a flow rate that is too low, you could end up taking alot longer to rinse in some cases. However, have the flow rate too high and you could end up using all your water up too quickly as well as 'pressure washing' the customers windows. Customer feedback we receive is a good sensible rinse will help you clean quicker.
2/. What size hose are you using? Using a smaller bore hose such as 6mm will actually save your water consumption whilst maintaining a pressurized flow from the pole, thus giving the effect of a slightly stronger rinse. So customers who use a 10lpm pump with a 1/2, 3/8 OD style hose would use gallons of water unnecessarily.
As a point of reference, the GrippaMAX systems use a 6lpm pump with the Liquid Logic controllers - something around the 25 - 45 FLO rate is the average our customers tell us they use based on a 6mm Microbore 100 metre hose reel setup.
So if you wanted to experiment, you could turn the flow rate up on the controller to get closer to the maximum 6lpm /100 psi output, and you would likely find on '99' with a 6mm hose that the pressure was just way to high (subject to your particular method of cleaning, some customers love to use a large amount of water).
In summary, if a customer asked us for a 10lpm pump, we could supply. Would we recommend it? Not really. I think we have probably sold 2 in comparison to hundreds of 6lpm pumps, and i think the same effect can be achieved with a correctly plumbed system.
Hope that helps you,