Actually your overclocked i7 is quite a lot faster than the FX 8350 at stock clocks and probably a bit faster than an OC'd FX 8350.
Your current CPU will have no problem with dual Titats, let alone dual GTX 670's.
And PCI-E 3 makes absolutely no difference compared to PCI-E 2. The difference is less than 1% so the AMD platform will NOT cripple you.
There is a difference. When GPUs in the future will be released, they will have a higher memory bandwidth and PCI-E 2.0 is already crippling some of the AMD GPUs by a little as you just mentioned. Only by a percent or two, but that number will increase, as the bandwidth of the GPU increases.
So I will definitly say it's a cripple.