Now graphics cards are a whole other monster in and of themselves, what are you doing besides Far Cry 3? I just looked up the recommended specs on the game and they ask for a GTX 680 to run it on high settings. Now don't get me wrong a 680 would definitely be an upgrade, but a rather costly one, and honestly it might start to become bottle necked by your CPU. Also the 680 runs about $500 so there's that. If you want to save a little money go with the 670 and overclock it, the performance level comes up to the base level of a 680 on a good OC.
Now this is the 670 I would recommend simply because Gigabyte cards are great and the cooler is fantastic for a higher overclock.
That's about all I can say on the Nvidia side of things, I'd rather have someone with more experience with AMD cards come tell you which ones to get there and then tell me I'm wrong about Nvidia and that they suck but again, personal preference.