If 3 is the max you run it then 3 is fine. As Dave said you just want to make sure it can handle the max it will run at. I only change the settings on my PV when I run at low feed rates due to spring or fall weather. That way when the stove is feeding at very low rates (mostly running on min feed rate)I won't lose as much heat out the PV.
Overall though the PV will be set and forget for the rest of the winter. One thing does happen to mine though, as it gets more fly ash and the oil in the motor is being used up in the PV I have to increase the setting slightly, so just keep an eye on it. After I blow out the fly ash and lube the motor I have to decrease the setting quite a bit.