Ok so get a GTX 760 atleast, as the other parts of your computer are high end and to take advantage of that you should also choose a high end Graphics Card.
GTx 750 ti comes in budget , i use it and it great for 720p Ultra 60 fps. So for 1080p gtx 760.
If you are going higher resolution than 1080p get higher card aswell. r9 280x i would suggest.