My issue is I can't go back past 13.1 since I have 4 7950s and 1 7870 Tahiti(7950 with cores cut down). The 7870 wont install on anything earlier then 13.1.
I understand that this board has enough PCIe slots, but I don't think it's a good idea to use that many 1x slots. I don't know that much about this, but apparently you can fry the motherboard with too many cards. 16x provides more power than 1x (I assume). You should look at this one: http://pcpartpicker.com/part/gigabyte-motherboard-ga990fxaud5
That being said, it's your build to do with as you please. As for me, I'm looking into buying powered risers to be on the safer side.