What's up with my 7950?

[Originality]

GPUs: 2x sapphire 7950 3L
Mobo: GA-Z87X-UD4H w/ SATA power cable connected
PSU: Seasonic X-850
Running Windows 7 x64 & CCC version 13.12

"top" card gets 69C w/ ~530kH/s @ Intensity 18, 925 core, 1250 mem, 1.100V and is plugged into the monitor via DVI
"bottom" card gets 66C w/ ~540kH/s @ Intensity 18, 925 core, 1250 mem, 1.100V and is headless

The "top" card will make the display driver stop responding if Intensity or Clocks increases
The "bottom" card can be increased to ~620kH/s @ Intensity 20, 1050 core, 1500 mem, 1.100V

This isn't a PCIe slot problem, because I tested it with all 3 x16 slots, all the same results as "top" card.
This isn't a GPU problem, because I tested all 3 x16 slots with the "bottom" card and got the same results as "top" card

Any help?

[Originality]

I got moved? o_o