PCPartPicker part list / Price breakdown by merchant

This build will run anything with high-ultra settings including new AAA games and will give you ultra smooth gameplay with the high refresh rate of the monitor. The monitor takes some calibrating but has some nice features over the ASUS like blur reduction and better color accuracy. A single 980 is pointless over a single 970 unless you're playing BF4 multiplayer with the settings turned up, or other niche situations, you'll never see the notorious "3.5GB VRAM" deficiency pop up at all.

If your SO is near a microcenter, tell him to go in store and pick up the motherboard + CPU to get the discounted prices on both.

The build below is closer to the limit of your budget and will max things out at 1440p and has adaptive sync to reduce stuttering, creating a pretty amazing visual experience.

PCPartPicker part list / Price breakdown by merchant