I need a PC specifically for video and audio editing.
Do I look for PCs designed for gaming like a Cybertron (my thinking being that their video processor and audio card would be higher end than most generic purpose PCs like a Dell or HP -- and admittedly that thinking could be totally bogus), or do I just go for the high end PC with the fastest processor and high end video and audio cards? I guess to that same question, what exactly makes a PC a "gaming" PC in the first place?
Regarding the audio you have 2 options:
- Motherboard audio quality (some gaming Mobos have excelent audio)
- Get a high end sound card and connect it to the PCIe.
For video, you gota go full out on the CPU (Xeons, i7, AMD-FX, etc, etc). Basically, multi-core CPU with high speed clocks.
With that said, cut down on the GPU component. You can get a medium entry GPU for the use you are describing.
You are best off to build instead of buy one prebuilt as you will end up paying more for things you don't need, and still have to add in other parts.
blasc gave you a good amount of info on what you need.
For video editing I would go with no less then an i7 or Xeon E3. Both of these CPUs will give you 8 simultaneous threads (the AMD-FX 8xxx will as well, but wont be as powerful). The more threads the better on this, if you can afford a top dollar machine then it would be good for you to pay for the newer 6 and 8 core (12 and 16 thread) cpus.
Memory speed wont make much difference, just get a set of 16gb ram (2x8gb, not 1x16gb).
A high end GPU is not needed, the main helpfulness is if your software utilizes CUDA cores found in Nvidia cards. Only because of that I would then recommend a GTX 960 card. Otherwise something like a GTX 750 ti would be fully adequate.
If you doing sound recording then just go all out and get a good pci-e sound card. If not doing recording and just modifying audio digitally then your better gaming motherboards will have decent enough audio for your needs.