i love the idea but i'm affriad you're going to melt the milkcrate!
How much distance between the PCI-e connectors on the GPUs
and the corresponding slots on the mobos ? It looks like more
than a regular PCI-e extender is allowed to go to.
Two out of my four rigs ended up having one GPU (usually the left-most card, sitting to the left of the CPU) that couldn't reach the closest PCIe slot.
I simply daisy-chain the extenders. In both cases, I've used an x1->x1 extender connected to the logic board, then the x1->x16 extender into the GPU.
Whether this would work for the *really* high current draw GPUs is a matter of experimentation (with a fire extinguisher handy...
) - but I've had an overclocked no-name 5830 (with big protruding heatpipes - the ones that look good but don't cool well) connected this way for weeks at full output. I don't have wattage figures for the individual cards, but this particular card runs 300-303 megahash/sec.
It must be drawing *some* power through the PCIe slot as well as the two 6-pin PCIe power cables - and it appears that the x1 daisychain is up to the job. I've inspected the cable today because of some unrelated failures in other cards, and there's nothing that'd indicate obvious overheating in the extender.
I probably wouldn't stick a valued high-end card on the end of a daisychain though... and I wouldn't try daisychaining three extenders. BTW, none of my daisychains used the Molex-augmented extenders... just plain dual-layer ribbon cable.
As always, YMMV, I'm not a qualified Mining Hardware Engineer Professional etc.