Custom PC for Gaming Question

My recommendation:
PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i7-6700K 4.0GHz Quad-Core Processor ($419.99 @ Newegg)
CPU Cooler: CRYORIG H7 49.0 CFM CPU Cooler ($34.50 @ Newegg)
Motherboard: Asus Z170 PRO GAMING ATX LGA1151 Motherboard ($162.98 @ Newegg)
Memory: G.Skill Ripjaws V Series 16GB (2 x 8GB) DDR4-2400 Memory ($84.99 @ Newegg)
Storage: Samsung 850 EVO-Series 250GB 2.5" Solid State Drive ($77.99 @ Amazon)
Storage: Seagate Barracuda 2TB 3.5" 7200RPM Internal Hard Drive ($67.88 @ OutletPC)
Video Card: MSI GeForce GTX 980 Ti 6GB Video Card ($649.99 @ B&H)
Case: Phanteks Enthoo Pro ATX Full Tower Case ($99.99 @ Amazon)
Power Supply: EVGA 750W 80+ Bronze Certified Semi-Modular ATX Power Supply ($73.98 @ Newegg)
Optical Drive: LG GH24NSC0B DVD/CD Writer ($16.33 @ OutletPC)
Operating System: Microsoft Windows 8.1 OEM (64-bit) ($95.99 @ SuperBiiz)
Wired Network Adapter: TP-Link TG-3468 10/100/1000 Mbps PCI-Express x1 Network Adapter ($11.59 @ OutletPC)
Total: $1786.21
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-12-10 01:45 EST-0500
 
Solution
Why are you getting an add-on ethernet adapter when the motherboard has one? Get a WD Blue or Black instead of the Seagate Barracuda, more reliable.

As pointed out above, single 980 is a better idea than dual 970s and you don't need that much RAM, at least before you use the system for a while and see how it runs. Two 8 gig sticks is plenty, even 8 gig is enough for most use.

I'd also get a Blu Ray player/writer instead of a DVD one to give you a bit of flexibility with movie playing.