I love it when people just throw darts in the dark...
A couple of questions need to be asked before the question should be answered. Specifically, what is the source and quality of the video being edited? How much video editing is being done, i.e. a few a day, one or two a week, one or two every few months, etc... And what is the end use of the video's, i.e. saving to computer for local playback, uploading to youtube or similar, creating mobile video for tablets, smart phones, etc..., burning to DVD/Blu-Ray.
For a lot of people, a Z77 is fine, but X79 does have 6-core (& 8 core*
) options to allow for faster encoding. AVCHD source content is notorius for needing a lot of CPU processing power. *ASRock has enabled the use of all current LGA-2011 8-Core Xeon processors on their X79 motherboards, not that most people can afford a decent one....
I had a herp-derp moment. The X79 platform and its processors don't have any IntelHD GPUs on them, meaning you're forced to buy a video card and you won't get any compute acceleration that could be used for media work. So I think for performance reasons, the Z77 platform would be better.
If he's using Adobe it doesn't matter, they do not support transcoding on GPU's anyway, only a few in-program accelerations & 90% of those require an ATI or nVidia GPU. Adobe uses OpenCL(ATI) or CUDA(nVidia) to accelerate a few dozen in-program effects, transitions, previews & playbacks, neither of which are supported by Intel graphics. OpenGL which Intel does support is only used for a very tiny number of in-program transitions & in-program preview/playback.
A tried and true litmus is really simple, if you have to ask about X79 it's not for you. You know what I mean!
We are the 1%.... just because we don't have to ask, doesn't mean that everyone knows.