The Z820 with dual 3.1GHz CPUs (16 cores total) can play back 5K in real-time. However, that's all it can muster when working at such resolution. The RED Rocket takes a huge load off the CPUs. The wavelet decompression is the resource drain when it comes to processing R3D files. It's not the debayer process, that's relatively simple and something GPUs can accelerate and often do in some apps, but RED has left their debayer processing internal to their own API's.
I'm hopeful that we'll see more hardware acceleration options in the near future with the Xeon Phi and upcoming Tesla compute options as they should be better suited for wavelet decompression.
FWIW, I'm running an EVGA GTX690 in my Z820 now. It's giving me the best overall performance per dollar per slot of anything I've tried. Premiere likes it, AE likes it, Resolve likes it. These new nVidia Kepler cards are similar in overall CUDA performance compared to the previous Fermi architecture, now that drivers are getting better optimized. If you need double precision or better FP32 or PF64 computations, the Fermi-based CUDA cards are still a better choice. However all the apps I'm using, which include those I just mentioned above, are all single-precision and scream along just fine.
nVidia will be releasing new Tesla cards based on Kepler over the coming months and the Tesla K20 due early next year will support higher precision. We should see updated Quadro cards after that.
After flopping back and forth between the GTX690 and various other GPU combinations, this is what I've settled on. The Quadro 6000 + Tesla C2075 (or GTX570 companion) was also a compelling dual GPU solution for Resolve, but after seeing the GTX690 in action here and it only taking one slot, I couldn't pass that up. The Quadro does hold an edge for complex OpenGL visuals and massive computational sets as it has more onboard RAM with ECC. But I'm not really needing any of that at the moment with this system. Precision on edge calculations and anti-aliasing or general pixel-precision within OpenGL, as well as performance with many legacy OpenGL operations like glReadMemory and glReadPixels are faster on the Quadro cards. If I were spending most of my time in Pro/E or SolidWorks or even XSI, I would stick with the Quadro. But this is primarily an Adobe CS6, Redcine and Resolve workstation. GTX screams.