KWin Can Cause A Performance Hit Too, But It's Different From Compiz
There is nothing new with the Unigine Sanctuary or Tropics results.
With Unigine Heaven, the Catalyst driver experienced a performance hit when running KWin where no frame-rate drop was experienced when running Compiz. With the NVIDIA driver there was an equal performance hit with KWin/Compiz when compared to Metacity.