Devastator is shaping up.
The seven 980Ti's have been downgraded to three 980Ti's...with cooling issues since they aren't on flexible cables of course. Parts ordered that MAY help with that (short PCIe PCB risers and 25mm tall motherboard standoffs to mount the 'tall' card to the case's screw holes).
The processor is a 12 core/24 thread Xeon E5-2658v3 at about 2.0GHz. Without HT enabled, it tests out as just a fraction faster than my i7-5820k
with HT @3.3GHz, using Cinebench. For the price I got it at, I'm thrilled that it matches the i7. $163 from Ebay.
Cooled using a Cooler Master 212 EVO with additional fan. So far runs pretty warm, upper 50's. Hoping to break in that thermal compound soon. $31
Motherboard is a MSI X99A SLI Plus. Seems identical to the discontinued X99
S that the twins are using, except has USB3.1. $200
No optical drive is necessary, but may toss in a spare DVD burner. Hard-disk-duty is handled by a cheap M.2 SSD, 275GB Crucial MX300. $78? Tried using a spare 500GB 7200rpm HDD...but I'm spoiled by the response time of a SSD.
RAM is 16GB (4x4), Xeon won't allow anything other than 1066 speeds. May try to see if the timings can be improved though, in the future. $-spare parts-$
Was going to be a semi-custom open case due to the remote mounting of the seven GPUs, but now not needed so I put it in a Cooler Master HAF XB cube. $90
PSU is a Corsair AX1200 Gold. $-spare parts-$ The PSU doesn't fit inside the case, and the case already comes with a bracket that makes the PSU stick out 30mm or so in the back. The same order of standoffs ($6) for the GPUs will be used in the back to attach the PSU bracket to the case. Gonna look even funkier.
Quick run of Folding at Home showed 600k ppd per card, due to being the 4996 FTW version cards with higher clocks, from EVGA, $351 each from Ebay. Got them from a seller who had a fleet of them, for use in his personal LAN gaming room, for when he had few friends over. Sheesh, and I thought DC was an expensive hobby! I think he had 7 entire high end systems in there!
Please, no one total this up. I don't want to know. Really. I think it's a pretty good deal though for the GFLOPS.
EDIT: Several minor edits were made to include additional information.