some links for 8 gpu
http://cryptomining-blog.com/tag/8x-gpu-mining-rig/
https://devtalk.nvidia.com/default/topic/738070/cuda-setup-and-installation/8x-gpu-gtx-issue-under-windows/post/4208565/#4208565
http://forum.ethereum.org/discussion/5195/riser-1-to-3-pci-e-1x
http://forum.ethereum.org/discussion/comment/34553/#Comment_34553