Create an empty scene with the standard spectral atmosphere and do the HyperVue render again. It's quite likely that the computers will now render at approximately the same speed. If not, then there is a problem I can not explain.....

Some tiles are easy to render, some tiles take hours to render, all within the same scene. It just depends on what they are rendering!
The first tile might be some grass and plants (easy) while the next 3 tiles are water, with reflections, transparencies, bump and objects submerged in the water. That can take a while. In the mean time the first computer dashes past the hard bits and renders the rest of the scene, apparently in no time......