Jim, besides from piston sizes keep in mind 996 calipers require larger rotors.
Larger rotor diameters increase brake torque.
So (from theory) with larger discs you need smaller piston sizes if the front brake
has to mate existing rear brake system to preserve balance.
The NQSBBK provides slightly larger pad area and much better pad pressure
distribution, so increased brake caliper efficiency. I bet the slightly smaller piston
area won't weaken balance.