Well, I'll go with what my father, who owned and sold two concrete companies over the years said to do which was 4.5"....
The added water was not for finishing. It was to make it easier for them to get some out of the truck and the 4.5 was thick. They did it in one spot, that spot is low. It's low because it dried at a different rate/amount than the rest of the slab.
To date, I don't even have surface cracks that I have noticed.
