CPUs in a 4 socket system cannot yield 800K PPD or more. They might be able to snag 200-300K PPD tops if they use 8 core SB-E and 8-core IB-E silicon. That production actually comes from systems that are running several GPU in tandem with their CPUs.
My lowly, 660Ti manages to produce 30-40K PPD. The higher-end stuff from Nvidia and AMD yield even more PPDs. Just throw a few card in a workstation chassis and you have something that pump an easy 500K PPD from the GPGPUs alone. Thermal management is tricky, but doable.
I am still hoping to build a 2P IB-E at some point, and put two 7990's (or more) in it. But I might need to put it in the refrigerator!
The system is going to be loud at load though.
Not if it's in the refrigerator!
Seriously though, I really like water cooling because it's efficient and QUIET, but extracting heat from two CPUs and four GPUs (running at 100% utilization) with water will likely require two or three loops with their own pumps and radiators, or one very long loop with a huge radiator and probably an expensive case from Mountain Mods to support a 9X120mm radiator.
Assuming proper airflow through the radiators and decent waterflow to match, this would cut WAY down on the noise. That many processors in one box will necessarily generate a noticeable amount of heat and will consume a noticeable amount of electricity. I think in another thread, I said I calculated just under $100 per month added electrical cost just to run a 2P box with two 7990 cards (4 GPUs) folding 24/7. This does not account for how much harder the house air conditioning will need to work to overcome the extra heat, so I think it would probably be reasonable for me to budget $110-120 to run such a machine in my kitchen or a spare bedroom. Not a trivial amount of money; can't swing that just yet.
But said box might generate 650,000+ PPD, depending on the CPUs and GPUs chosen for the build.