" For animation, I think it's quite simple : with 10 identical PCs, it would be about 10 times faster than with one PC :)" I doubt it. I think your figures reflect the true nature of distributed rendering efficienty. I've had a deal of experience working with mental ray on farms of up to 1500 nodes. In the early days we looked at distributed rendering - which is what Vue/Rendercow does. The ratio of rendertime to number of machines is never linear when you're rendering in this way. hard truth, this kind of rendering is nowhere near as efficient as rendering one complete frame per machine. If you start scaling this up to movie size then the fun really starts. I'd be willing to bet once you get up into the hundreds of CPUs the time per frame will actually drop below the time it takes to render one frame on a single machine. Rendercow rendering is attractive but it's not effiicient.