I bought four of the low-end model Octominer built from their very first pre-order batch around 2 years ago now I believe.  They've all been working great for me but perhaps I simply got lucky as I've heard similar complaints as the OP's from others that purchased on a larger scale.  I only connected two of the 6-pin connections to the motherboard which is what they list as the minimum.  Perhaps that limited the power the board was delivering to the pci-e slots, maybe I really did just get lucky on my four boards.  All I know is that if they had fit in the server chassis I had built I would have bought at least 100 more.

Bottom line is I would rather deal with finicky motherboards (which I didn't even experience.  They were plug and play for me) that I know will work once setup as opposed to 8x miserable risers that even after I finally get connected properly will eventually die in unpredictable ways giving seriously cryptic errors.

-TBT