Also, if I am not mistaken, which I might be, I don't believe that you can run more than 6 GPU's on a machine. Like I said, don't quote me on that, but the 7 PCI slots would be a waste I believe.
windows nope ;/
windows WILL NOT recognize more than 6 GPU's. fail ;p
linux on the other hand... i have heard users having up to 32 GPU's running on a linux machine with "EthOS" (ubuntu 14.04)
There are definitely powered risers for 16x to 16x risers. Should be fairly easy to find. Here is a website that seems to be good gpushack.com.
Ok, that was where I was thinking it was from. Can't run more than 6 GPU's on windows. Did not know that about Linux though. I remember seeing an attempt at a huge backplane to run a bunch of GPU's, but I am pretty sure that they never got it going.
ooo yes i would also recommend gpushack they have some dece stuff, great range for what you wanna spend
it's a shame farms like genesis weren't as transparent as they claim, would be interesting to know how the "big boys" are running their gpu farms.
(all headless and remote access i assume)