Good question, as to what I do! I'm a colorist, I work with HD video and color correct that footage. My software of choice is Davinci Resolve. If you are super curious, they have prelisted 'certified' components here:
Resolve Configuration
The very basic corrections need one gpu for the gui and another for the processing. The 690 is great, as you could have 2 of these cards and because there are 2 cpus in each, you could have 1 for the gui and 3 for the processing. Anyway, to get back to your question, I need these HD and 2k videos to run at full playback speed and resolution in real time as I make the corrections to the video.
Right now I have a quadro 600 and a gtx 680. I'd like to have a little more horsepower though. The RedRocket would set me apart, but that is a very very expensive (overly priced imo) piece of hardware. It's a bummer too that I can't export Apple Pro Res video from a PC, but that's something else entirely. I would have stayed with Apple, but the power you can get out of a PC exceeds that of a Mac, and the price is very different indeed.
Also, I wanted to mention, that in different builds of the Davinci Resolve models they have dual socket processors, which I don't know anything about those types of mobos. What I hear from the techs at Blackmagic that make Resolve though is that the processor isn't the main thing, it's the GPUs. Some systems even have the Cubix addon, which starts getting way more expensive than I think reasonable, but then that's when I start charging for it.
The specs call for a MicroSupercomputer, but I believe that this is something I can figure out how to build myself. I've already built one system. A lot of how this program works feels very similar to how gaming systems work.
By the way, the chip I have on this system is the i7 3820 3.60 GHz, with 16GB ram (ripjaws I think?).
Have you seen the Sniper mobos that gigabyte makes? They work with the x16 in each slot. But you are telling me that wouldn't matter, as long as the CPU can handle the certain number of lanes, correct?
I think a lot of what I just wrote is all over the place, but also in its own way paints a picture of all the things I'm thinking about in how to create color and be great at my job. (I really like the Fractal cases, by the way, thanks for that. They look very work/pro).