I got more or less 30 fps with these settings:-
Of course, min fps dropped to single digit some times. But, gameplay remained more or less smooth throughout, so you should have a blast with the 7870CF with PhysX off. And you can turn off DOF to get clearer visuals and boost in the frame rates.
Options: Resolution: 1920 x 1080; DirectX: DirectX 11; Quality: Very High; Antialiasing: AAA; Texture filtering: AF 16X; Advanced PhysX: Disabled; Tesselation: Enabled; DOF: Enabled
Of course, min fps dropped to single digit some times. But, gameplay remained more or less smooth throughout, so you should have a blast with the 7870CF with PhysX off. And you can turn off DOF to get clearer visuals and boost in the frame rates.