Because the low end standard CPU's, ie G4400 will not work beyond 8 GPU's, 9 MAX on windows. The SSD is for Swap File which is quite large for 24 GPU system. The CPU that performed best for price was the i5 6600k. We also factored in each components overall rating, quality, performance and price with the intention of providing quality, stability and lifespan.

Then you take into account, say $350 for standard cheap MB/CPU/RAM/SSD versus $820 for the quality (and that actually runs stable) That is a fraction of the overall cost. GPUs are the primary component here and I found that the MSI GTX 1080ti 11G was the most performance and rock solid stability. Yet when I tried to put in a smaller overall footprint I had a heat issue. There for I tested the MSi Seahawk. I was not only able to make the overall system smaller but packing the GPUs closer, I was able to run the system at higher rates due to the liquid cooling and still have great stability with a maximum HASH/Power. At a cost of $50 more per GPU - it's was definitely worth it. The GPU's alone are ~$20k. This system is optimized down to a single (not 4 or 6) MB/CPU/RAM/SSD and 4 PS. This increases profits as well.