The index man! That is a title I will bear with pride.
To be honest, this is the first I've heard of CDF but from what I can gather, its aim is to track the index. I'm not sure what makes you think it performs better than STW: if anything, it should slightly underperform STW as STW's fees are lower (approx 0.3%pa versus 0.6%pa for CDF).
Hope that helps.