No need to run pumps at max speed. At some point the gains become minimal and noise + wear on the pumps is not worth it. He isn't running a single d5, but dual pumps that have higher head pressure than a d5 so he doesn't need to run full speed to get good cooling. Most blocks have minor gain between 0.5gpm and 1gpm and very low gain above 1gpm.Pumps should also run max speed.