Willie may have since changed his mind but he did comment once, maybe 4 years ago, "I find large discus do better in a 75/90 gal tank when there's strong current. I often add a powerhead, by itself or on top of a double stack sponge filter, to these tanks. While beginner books say that most of oxygen diffusion occurs at the surface, I question this statement. Discus in the powerhead tank clearly swim more and eat more vigorously. A friend who only keeps large Africans notice the same in his tank.
We keep large fish in a relatively small tank and extra water movement is usually appreciated. "