You have to dig into each separate program. Find out what they need. How well are they coded for multiple threads? Hyperthreading? Are there any that benefit from CUDA? Crossfire support?
It's a lot of googling and I could do it for you, but really it's a process best left to you.
In the end, each user has their own mix of programs and workflow, and so each will have different priorities. You need to figure out what questions to ask first, clearly.
Alvin Smith is a good person to consult here. I will link you to a few threads to peruse where he helps out with a few builds. Feel free to drop him a PM and ask him to respond to this thread. http://www.tomshardware.com/forum/300314-31-high-personal-workstation-guidancehttp://www.tomshardware.com/forum/284286-31-rendering-workstation-supercomputer