I'm building a multi-GPU machine for scientific calculations. I'm going to pair a Xeon E5-2620v3 CPU with the Asus X99-E WS motherboard to install 3-4 Titan X GPUs. The CPU provides 40 PCIe lanes and the chipset provides additional lanes, so that one can run up to quad x16 setups on a 40-lane CPU. What bothers me is the theoretical performance impact originating from the limited bandwidth. How critical is that for applications with almost 100% GPU-bound loads if GPUs will be constantly loading data from RAM? Should I rather go with 2 CPUs?