There was a study done at the University of Limerick a while ago where some black belts from a local ITF club done straight punches against a sensor to measure the force. They done punches with the sine wave and without the sine wave.
They found that on average the punches from the Sine Wave were only something like 0.16% harder than the punches without the Sine Wave. Although this isn't a conclusive study because it was pretty small, it still raises doubts about how effective Sine Wave was about generating power.
I think the studies were bias; an ITF school trying to prove that SW is better. Did anybody in the study actually hit harder without SW? And that after all the punches were done they just averaged it? I would be more readily to believe such a thing if the participants were all of equal height and weight. All had equal years of practice in their arts and included ITF, WTF, Karate, Boxers, etc. In fact the boxer probably could hit harder which than I guess would prove that all other punching arts are less; correct?