I am avoiding AC unity like the plague right now, as I hear it is buggy and terrible on AMD hardware. Anyway, I just gave my buddy my R9 270x, as I am going to replace it with a GTX 970. CPU BOTTLENECK, you may say. Well, after doing some searching and performance evaluations of the X4 860k, this CPU won't bottleneck single GPUs (290x, etc.). It definitely will if running SLI/Crossfire, but I am not keen on multi-cards for a number of reasons.
I will maybe give ACU a try once the worms get run out, but I am more interested in Far Cry 4 right now. To my understanding, as well as my buddy's who is a hardware snob, virtually all games 2013 and later, are GPU bound. As long as your processor isn't so old or slow that it will bottleneck the card, there should be no issue.
Example review: "If you're a gamer this CPU will do just fine. All games now are GPU bound. 2013 and up anyway. I have been running nothing but bench, calculating, heat, and operation test since this CPU arrived. If you are worried about GPU bottlenecks, don't. It will bottleneck a 290x in crossfire and maybe a 28x in crossfire, but single GPU testing showed no bottleneck. If you don't crossfire the most expensive video cards on the market then you should have no issues in gaming. If you are such an enthusiast that you have a 290x crossfire setup, then you probably was not looking at this CPU anyway."