I'd go with a 390 card myself, you won't need the 8gb at 1080p but the 390 seems to be performing notably better in dx12 than the 970.
If that x99 board supports m.2 drives at pcie x4 speeds consider one of the samsung sm951 drives, check if that mobo likes to boot from them though. a bit more expensive but much faster. Note there are nvme and ahci variants, prolly want the nvme if compatible.