This is correct. I'm using an i7-2600k @ 4.8GHz with 2xHD7970s @ 1920x1200 and with PhysX set to High (=2 in .INI file, same as setting via game menu... no need to pretend it's a "hack," gaming journalists, just select the option like a normal person) the game runs great until you get into a heavy firefight with grenades, shotguns and rockets. FPS will tank to 14-15 during these scenarios until the particles fade away. Setting PhysX to medium helps a lot, and setting to low obviously results in 60FPS 100% of the time on this rig.
Whatever test they used for this benchmark was obviously not actual gameplay, or they didn't actually enable high level PhysX effects.
Also of note, even with PhysX set to high, my CPU loading never exceeds 40%, and GPU loading never exceeds 60%. Reeeeal efficient.
Fun game, though.