I like my polished aluminum Two Bros cans. They sound wonderful, and look it, too. Especially with my polished wheels (black & gray 99 Busa). I don't know if they produce any more power or not and I don't really care. Power is just not an issue on this bike for any kind of semi-normal street riding, which is what I do with it.
I happen to like the symmetry of two cans, so I never considered a 4-2-1 system.