No reason to go to a heaver cone. And the Aluminum doesn't have the natural sound or articulation of details like the paper cone.
Not to mention that the Rythmik 12" aluminum-coned woofer can't be used above 120Hz (that's the highest x/o setting on the Rythmik Servo plate amp. The woofer actually shouldn't be used even that high), and, most importantly, can NOT be used OB. The GR SW-12-16FR and SW-8-16FR woofers are the only Servo drivers with the technical properties that make a driver suitable for OB use.