MSI X370 SLI Plus 3 Way GPU (non-SLI)

Solution
It will operate in PCIe 3.0 x8/x8 + PCIe 2.0 x4. That chipset is not optimal for all those GPU.

If GPU Rendering is your goal. consider x99 motherboards with a cheap Xeon. This supports x8/x16/x8 Mode.

PCPartPicker part list / Price breakdown by merchant

CPU: Intel - Xeon E5-2603 V4 1.7GHz 6-Core Processor ($209.99 @ SuperBiiz)
CPU Cooler: Cooler Master - Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler ($24.89 @ OutletPC)
Motherboard: MSI - X99A SLI ATX LGA2011-3 Motherboard ($146.98 @ Newegg)
Total: $381.86
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-09-25 21:04 EDT-0400
It will operate in PCIe 3.0 x8/x8 + PCIe 2.0 x4. That chipset is not optimal for all those GPU.

If GPU Rendering is your goal. consider x99 motherboards with a cheap Xeon. This supports x8/x16/x8 Mode.

PCPartPicker part list / Price breakdown by merchant

CPU: Intel - Xeon E5-2603 V4 1.7GHz 6-Core Processor ($209.99 @ SuperBiiz)
CPU Cooler: Cooler Master - Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler ($24.89 @ OutletPC)
Motherboard: MSI - X99A SLI ATX LGA2011-3 Motherboard ($146.98 @ Newegg)
Total: $381.86
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-09-25 21:04 EDT-0400
 
Solution