What MB for 6950 CF

I'm planning to go eyefinity with 6950s in CF.
My current setup:
CPU: AMD 720BE @3.4
RAM: 4GB mushkin DDR3
MB: Gigabyte GA-MA790XT-UD4P
HD: WD 640GB
PSU: 550w BFG
GPU: EVGA GTX260
Display: 24" Dell LCD ST2410b

Upgrading to:

CPU: AMD 955BE-970BE
RAM: 4GB mushkin DDR3
MB: Gigabyte GA-MA790XT-UD4P
HD: WD 640GB
PSU: 750x-850w psu
GPU: 2x 6950
Display: 3x http://www.newegg.com/Product/Product.aspx?Item=N82E16824236102


I'd like to use my current MB if possible because I have another MB I can put the 720BE in and would like to make use of it if possible. My question is that the PCIe slots on my MB are 1 16x and 1 8x. Do I want a MB with both PCIe slots being 16x or does it matter and also all the 6950s say 2.1 PCIe and my MB says 2.0 is that a problem?

I'm not sure what PSU I'm getting but I know I'll need a new on to go CF, any suggestions would be a great help.

I know theres a lot of people in here with CF setups that could answer my questions. Really confused with all the MB options out there and could use a little guidance.

Looks like according to this article x16/x16 vs x16/x8 makes no real world difference so I'm guessing using my current MB wont be worth upgrading. those tests were done on SLi 480s and CFX 5870s but I assume the results would hold to current gen cards.