Please post full specs of your computer and what budget you have so i know what gpu would go along with your cpu and psu and what price range to look at.
If you have a good cpu that wont cause bottlenecks and a good enough psu a gtx 970 or r9 390 will definetly run fallout 4 at ultra on 60 fps, even the 960 and the 380 may be able to do it but we cant know for sure since they havent even released the pc system requirements