My current development/rig hardware:

• Asus X99-E WS Motherboard
• CPU: Intel i7-5960X, 8 hyperthreaded cores for 16 virtual cores
• 32GB Memory: Corsair DOMINATOR® Platinum Series DDR4 2666 (PC4-21300)
• Samsung 950 PRO Series - 512GB PCIe NVMe - M.2 Internal SSD
• Ableconn PEXM2-SSD M.2 NGFF PCIe SSD to PCI Express 3.0 x4 Host Adapter Card
• AMD EyeFinity (X11 video card)
• GPU compute cards:
  • MSI GTX1080 Seahawk X on SDR box
  • MSI GTX980 on Reference box
• Power Supply: Corsair AS1500i
• Corsair Obsidian 900D CC-9011022-WW System Cabinet Tower
• Corsair Hydro Series H100i GTX High Performance Liquid CPU Cooler

Additional info on the GTX platform is available here and here.

The Asus motherboard supports seven 3.0 x16 PCIe slots, as well as two 1GBit ethernet ports. Having a dedicated ethernet port for the radio is almost mandatory as the raw DFC samples pretty much saturate a NIC.

Note: GBit ethernet is just a stepping stone for development, the Minerva on the PCIe bus will soon replace the ethernet interface.

Don't skimp on the power supply, A CUDA card consumes a LOT of power. An 800-1000 watt supply would probably be more than adequate for a single GPU card.

My original hardware is described here. I have since upgraded to a more capable system to support R&D: