i had some what the some problem with my first rig evga x58 ftw3, i had to get 16x riser on the 3 pci e and one power 4 pin on my four card and i wouldnt get 100% on my 3rd and 4th card, so i ratter keep my rigs at 3 cards.

you could always get your self some use parts on ebay to run an extra card or 2 , did it my self got my self a dual pci e board for 50 bucks on ebay
and i was able to run 3 cards on it.