Are you limited by budget or unsure what graphics card will work without too much bottleneck?
Could go all the way upto a 1080Ti if you wanted to, subjective to some bottleneck in some cpu intensive games at resolutions between 1080p and 1440p.
A gtx 1060 would be a nicer upgrade if budget allows and performance relative to a gtx 980. 1050Ti is a bit faster than a gtx 770.