FWIW:-
I have recently changed from a softer pencil brush to a harder fan brush and I feel the advantages are:-
1. I am able to flick those pesky spider's nests away quicker.
2. I clean quicker
3. I use less water.
Without measuring accurately my 400L tank now nearly always lasts the day whereas I was going back and topping up quite frequently when I used a pencil/soft brush.
I reckon I use 50/70L less per day and I now feel that whereas I was going to get a bigger van to take a 650L when I'm scheduled to change vans in 2 years, I'll stick with another Doblo or whatever Fiat model is new by then.