Lots of good info here:
Optimizing for performance: Adobe Premiere Pro and After Effects
[Moved to Hardware forum.]
You would not want to run the GPU's in SLI or Crossfire. The configuration would be independent mode. The single CPU 6 Core workstation is the ideal point for CPU processing and configuration options. However a Dual Xeon would be the choice if the media was 2K+ especially Red. That will decide the best configuration options starting out. BTW you may want to check the forums out regarding the Open CL performance of CC before you decide that route. Keep in mind the Open CL programming for the MPE is in it's infancy and will take some time to optimize close to the CUDA performance.