I'm also interested on PCI-E 1x -> 1x risers with molex power connector. Doesn't matter if the slot is filed to accept 16x GPU because I can also do that easily.

Btw, is it enough to use only one powered riser per mobo thus meaning the power will be distributed to the rest of PCI-E bus by mobo or should I use all powered risers?
My config would be 2 X 16x risers + 2 X 1x risers, totaling 4 GPUs.

What is the actual limit on how many high-end (7970) GPUs should I use on one mobo without powered risers?