Like tecmo34 says, the space is just enough for install both GPUs, but you need rise the speed of both GPU fans.
Also, bear in mind that when you use Crossfire in that mobo, the USB 3.0 is downgrade to USB 2.0.
even in a x58 mobo will the usb 3.0 downgrade to 2.0 ??
Fish !! I didn't know that..