I don't want a twin disk because I've simply heard that on DSM's, they just aren't that smooth. They also cost about as much as a tranny. And I swear every time I read about someone installing them, they seem to always have issues and have to modify crap to make them work.
The Evo ones drive nice, but they cost even more than the ones for DSMs and they don't handle as much power as you would think. You usually have to goto a triple disc on an Evo, if you plan on making a lot of power.