With that size bioload and in a planted aquarium, I imagine you could get by with your current Fluval. Over filtration is always nice and only rarely is it detrimental (usually via flow and hurts the plants). We have a Fahaka and numerous Tropheus keepers will agree, if you have room under your tank then you are not filtering enough, lol. It sounds crazy, but very true. In my opinion though, I would be happy using a seasoned sponge filter in a planted 55 gallon with 30 Cardinal Tetra.
"In the land of the blind, the one-eyed man is king" Desiderius Erasmus