Twenty foot cables are long enough for the topology to matter. According to the Maxwell Equations, inductance is your enemy for speaker cables, and you don't have to worry about capacitance.
That means speaker cables which consist of two ribbons facing each other, like Goertz. As Elizabeth said, 12 AWG or better. Otherwise the highs will suffer.
That means speaker cables which consist of two ribbons facing each other, like Goertz. As Elizabeth said, 12 AWG or better. Otherwise the highs will suffer.