I do video rendering and editing. A lot of it. Make sure you have a quality software program written for 64-bit Windows (7 or 8) that will take advantage of extra memory, and also will run OpenCL, so that it will take advantage of not only all your CPU cores, but all your Compute Units on all graphics cards installed in your system.
I am running my setup with a budget build of an A10-6800K, and the software uses all 4 cores of the CPU, and all 6 cores of the iGPU that are within the A10. I also have a Radeon HD 7770, and the software also utilizes all 10 cores for that as well.
By making use of all the extra cores, I'm actually getting better rendering times on the same video than a friend of mine using an FX-8350 with the HD 7770, because it is able to take advantage of the onboard iGPU as well as the dedicated card.
Now, most people will say, "You can't crossfire an HD 8670D (the iGPU in the A10) with an HD 7770." They would be correct. I'm not crossfiring, however, I did not disable the onboard graphics either, so even though a game can't use it, rendering software, or any software, that uses OpenCL, can. When not using the discrete graphics card, if I use the iGPU with the CPU, then I get 185% performance boost over just the CPU cores alone. Adding in the HD 7770 to that 185%, and it is 2.5 times faster than the 185% figure.
I'm using low end graphics, for sure, but the motherboard, CPU, and discrete graphics card cost me less than $320 combined. I was on a budget, as the video work I do is volunteer work for a church that broadcast their services and makes DVDs available for purchase.
For professional video rendering, you should use the FirePro Graphics cards. With professional software that fully utilizes OpenCL, then the graphics card will be much more important than the CPU. With my lowly budget setup, the CPU is only going to do about 15% of the work or less. Adding another HD 7770 would make it do less than 5% of the rendering work.
You don't have to worry about CPU bottleneck if you're going OpenCL software. Just get the best graphics card you can.
Careful with the software you get. Some won't do OpenCL, and some will only work with Intel CPUs or NVidia cards. OpenCL works with everything, but the AMD cards shine better with OpenCL.
“If the automobile had followed the same development cycle as the computer, a Rolls-Royce would today cost $100, get a million miles per gallon, and explode once a year, killing everyone inside.” – Robert X. Cringely