ogormask, in case I missed it above, exactly how are the backplanes wired?
I'm in the middle of a similar build, with same power supply. But I haven't powered up the backplanes. Based on other postings I feel (and what I'm going to do) is one cable to 1-2-3-4-5; and a secondary cable to 1-2-3-4-5. There have been some posts about suspected connector issues with the Norco backplanes, thus requiring the redundancy. I know there were earlier postings about, nah the second molex is just for a back-up power supply; but the more I read, the more I think that the second molex needs to be powered off a second cable.
Just my thoughts.