Hello nlombardo896,
SLI connection is not necessary, it is related to the visualization and wouldn't help the processing. But you can still benefit from multiple GPUs. Number of CUDA cores (or shader processor units for AMD cards) will influence on the processing performance. The additional amount of GPU VRAM will improve the performance of the depth maps based mesh and tiled model generation as well as photoconsistent mesh refinement operation.
For CPU we still recommend to prefer higher CPU frequency (at least 3.2 GHz) with 6-12 CPU cores.