Does anyone know what fastest (or best for my needs) 48GB memory I can use with SR-2 without any bottlenecks?

I will be running it with dual X5690s and nVidia Quadro 5000. As you can tell I will mostly be using this system for Rendering and Video Editing.

I might add few GPUs later for games and assistance to Quadro 5000.

Cost of memory is not a big issue but will hate to waste bandwidth if CPUs can't handle it.

Thanks