Actually, I think it would work, based on th layout of the case. The only drawback for me is that my power supply is at the bottom but I'd still have room.
My motherboard has 7 slots and is set up this way starting at the highest slot;
1) PCIe x1 slot --- unoccupied
2)
PCIE 16x --occupied with my current 6950 ---dark blue in color
3) PCIe x1 slot --- unoccupied
4) standard PCI slot --- unoccupied
5)
PCIe x16 Gen 2 slot --- to be soon occupied with my NEW 6950----that will run in 8x mode ---white in color
6) standard PCI slot --- unoccupied
7)
PCIe x16 Gen 2 slot ----that will run in 4x mode ---black in color
So since slot #3 and #4 are not going to be used, I have the 3 slots needed (2, 3 and 4) to give the 3 slot occupying Arctic cooling fan enough room....but again, again it will be close because the next slot I need to use is the 8x which occupies the #5 spot.
If I can just figure out a way to run a PCIe x8 cable from the white 8x slot and drop it down a little....it would give me about a good inch between the two 6950's. Only problem is how to do it when the #6 position PCI and #7 PCIe slots are kinda in the way.
Here is a photo of the layout