Can speaker cables be too thick?

Hi folks, I've tried several speaker cables in the past, like the MIT MH-750, Wireworld Gold Eclipse, Ridge Street Audio, Pure Note Paragon and Cardas Golden Eclipse. I've been using these expensive cables until I replace them with ordinary 2x6mm2 OFC copper cables consisting of multiple small gauge solid conductors. These cables have the best tonal balance and they match very well with the speakers (Dunlavy SC-V). I use them in biwire fashion (each cable is 5 ft in length). What would happen if I replace them with even larger gauge copper cables, like 2x8mm2 or 2x10mm2? Would the sound improve further with the larger gauge cables? What sonic characteristics can be heard when the speaker wire is "too thick"?

Chris