goku1234567890 :
OK seriously if you wanna play watch dogs and next gen games you need atleast 6 GB ram. And getting the r9 290 or 780 is not totally necessary. Although both are great cards the r9 280x will do fine for you, simple as that. If you looking to throw money sure go buy 780 or 290. Another advice go with r9 series as they have mantle technology and it is giving an edge as compared to nvidia. Go will get higher frame rates in game by mantle supported games and watch dogs is one of them. Also you won't be needing overclock with these kind of graphic cards, so even though you are think of overclocking i overclocked my r7 250 upto 20%. And i am not a fan boy of Amd, i have used both the Nvidia and Amd ones and both are proven great and i have even played sleeping dogs on nvidia geforce 210. Any questions left here.
Mantel is useless right now, and wont be good for another year at least and even then, directX 12 will be released and that might just blow mantel out of the water. Also get a 770, its going to be cheaper since it comes with watchdogs for free since you all ready plane to buy it, its like a $60 off coupon on your GPU. If you like recording game play as well, then Nvidia is going to be great since it allows shadow play.