DMM,
It depends if you have an optimistic or a pessimistic point of view :) Personally I think seeing from the POV of the fastest computer is more realistic. After all if I could render on one computer only, it would be the one chosen. So all additional gain should be compared with this one.

JavaJones,
The overhead here is negligible. The scene is copied once on each cow at the beginning of the render. The image resolution of the frames is small, so sending information over the gigabit network is not an issue. And the HyperVue manager is really a Quad-CPU. At the beginning of the render sending the scene and all the textures is done in a few seconds, and the individual frames are saved only at the end.