so if i would build such a system, i would only put 3 vegas in.
or change the motherboard into the asrock taichi or the msi gaming pro, which have anaugh space for the cooling of each card.
And the Fans... you will need much of it, but you will need realy fast ones to get the heat in the case under control.
And then this will be really loud
what case u want to use?
corsair carbide, thermaltake view 71, rosewill nighthawk or b2 spirit. if i build it
Im trying to price everything out right now, the main problem is getting GPUs somewhere near its sticker price, cuz im not paying over $1000 for a used vega 64 if the MSRP is $499-$599
the expensive option is going for a digital storm build, but with GPU prices right now its pretty close...
EDIT: I really don't care about fan noise, i actually like it, i have a fan in my room at night at all times even in the winter. I don't mind the heat either, i only care about the heat for the computer/mining rig -