the 260x (not the 250) of your original listing should be able to play watchdogs on medium at playable framerates. i'm not sure how much the i3 will hold you back though. a 270x is capable of 60fps at high settings on that game, provided its not bound up by the cpu at all.
on low budget builds it certainly makes sense to consider amd cpus and a build such as the one i listed. completely your choice though.