I have a gtx 760, i get 60 FPS nearly everywhere in the game on 8 preset and cmaa. (of course barring the situations when the game engine is limiting, good example would be middle cap point in isle of conquest when everyone rushes flag).
You could find a used evga 960 and that is more than enough for what you play. I mention evga specifically because the warranty is linked to serial number on the card, and transfers owner to owner.
Whatever you do stick to nvidia for blizz games, the engine highly prefers nvidia architecture:
https://www.techpowerup.com/reviews/...X_1060/23.html
http://www.techspot.com/review/1209-...060/page2.html
If you could find a used EVGA 960 for under 100 bucks id do that tbh, here is how you check how long of a warranty is left on evga cards:
http://www.evga.com/support/guestregister.asp