Just a quick tip:
Some motherboards have difficulty recognizing 5 cards or require shorting some PCIe pins to get cards recognized with risers. The sabertooth I mentioned has always recognized cards fine for me, but make sure to check on other boards. X number of PCIe does not always mean you can run X cards without headache.
Yea, that's why I'm looking for another one. Current board has 3 x16's and 1 x1. One of my X16's will not recognize a riser. I'm running cards directly in the other 2 x16's and a card off of the x1 with a riser fine. Don't want to cram another card in there directly in the other x16 slot because of airflow.