Waterfarms are ideal for large plants. Growers who have to submit to inspections to check their plant count benefit greatly from flowering fewer, but larger, plants.
More, but smaller, plants make for a higher g/w/month number over ALL your watts, because the time component of that formula relates only to time spent in flower. So if you flower newly-rooted clones, the time spent in veg (not counted towards your ultimate yield) is minimized. Many, if not most, cash croppers run trays of small plants or some other SOG type arrangement, whereas most medical growers would tell you to give enough veg time to make each plant yield a bumper crop on its own.

With a 40 gallon res, fill it up all the way, add your calmag and base nutes, and check the pH and Ec. IF you start with a quality nutrient, that large volume works in your favor in a big way- you will find it to stay very stable over time. Sure, you are using a lot of ferts, but you get it back in yield.

'Better' is all relative to your goals, and to your space/time/startup budget restrictions.