Crossfire 7870 bottlenecks

[LoveTrain]

So I'm planning on buying 2x HD 7870 GPUs. One will be the Sapphire retail-OC version, and the other the Gigabyte retail-OC version and going crossfire. My motherboard will be either the ASRock 970 EXTREME4 or ASRock 990FX EXTREME3. My PSU is a Cooler Master M620 Real Power Modular - 620W. For CPU I'm thinking of buying an AMD Phenom II X4 965.

Now, first of all, I'm wondering what the differences between the two motherboards are, and how much of an impact they will have. Secondly, I'm wondering if the CPU will become a huge bottleneck? I believe it could be overclocked a bit without issues, but I'm wondering if I would have to really stretch it a lot to see any real benefit from the crossfire setup? Thoughts?

Thank you in advance.

 

[daswilhelm]

why are you starting a build with crossfire? thats more of an upgrade path for the future.

 

[LoveTrain]

Due to the fact that I can get the cards cheap.

 

[ajl2011shooter]

Go intel i5 and save yourself the headache. Even if you overclock the crap out of the AMD it will be borderline at best.

 

[LoveTrain]

Thing is the i5 CPU's cost about twice as much as the AMD Phenom II X4 965.
I am also still wondering about what choice of motherboard would be good, and when I would likely see a bottleneck from the CPU.