I just finished a session expecting the worst, but it's not that bad. Especially considering what I put up with in the past when I had a Crossfire setup. The driving performance is of course terrible, but playable. The on foot action is smooth to the point where I'm not going to spend any more time worrying about it. I'm not going to wait until the fall to play the port, and the PS4 version would not be an upgrade. The PS4 port runs at 30fps and I'm getting more than that on my PC (after the ini tweaks). No crashes, no long hitches or unplayable stutter, or anything else that prevents me from delivering non-fatal ass whippings. I got lucky.
Default settings (AA on / normal textures/detail / Gameworks off)
780 GHz edition
i5 750 (overclocked)
12GB memory
Windows 7
144hz Gsync monitor