The game runs surprisingly OK (20-30fps) with my 3GB 7870HD (which is below the minimum requirements) and an i5-3550, with everything on max (apart from shadows at high) as long as I don't turn on any antialiasing. The CPU usage is only around 40-60% (Though I've not been in Paris proper with huge crowds). Also, all options seems to have only moderate impact on performance - the difference between everything on low and everything on high is 10fps or so.
(This is on version 1.1 of the game and I haven't tried the new AMD drivers yet, since I consider just getting a 970 today anyway)
(This is on version 1.1 of the game and I haven't tried the new AMD drivers yet, since I consider just getting a 970 today anyway)