Real time video editing is one of those funny things where more than simple CPU grunt comes into play. The speed of the motherboard chipset is very important, as it the latency of the memory - low latency slower memory can be better than high latency high speed.
Also the actual editing software you use is an important factor as these are often optimised to work better with specific graphics cards.
Getting the balance right is quite an art, and there aren't many companies who can do it and get it right
These guys are one company that do:
DVC bespoke editing systems - laptops and desktops
It would be worth looking at the specs of some of their systems and trying to emulate them. Believe me when I say that their combinations of components are very specifically selected
PS
they seem to like this motherboard
GIGABYTE - Motherboard - Socket 2011 - GA-X79-UD5 (rev. 1.0)
along with a Intel Core i7 3930K Enthusiast Unlocked, S 2011 CPU