Specifically, 16GPUs is extreme, but for what the GPUs are being used for, do they need all of the PCIe lanes since they are not pushing pixel data? I ask as someone I know was into extreme mods. He built a rig that he'd plug into his dryer's 220v outlet to run. He also had PCIe break out cables to plug in multiple GPUs per PCIe slot on the mobo. Since the GPUs were only doing math for 3D rendering, he did not worry about the PCIe lanes. This was a really long time ago and I do not remember the actual speeds, but faster than CPU only renders.