FRONT: OEM steel rotors +/- $1000.00 (Suncoast) last about 16 hard track days, Hats = discs cost +/- $2000.00, but replacement discs are $1000 afterwards but should last 2x or 3x longer.
OK, if they are interchangeable, but I have found this on Rennlist:
The rotor fits over the hub just fine. No issues with spacing or offset. The 997.2 GT3/RS steel front rotors are dimensionally identical to the 997.1 PCCB rotors in how they fit over the hub and align laterally (using the plane of the axle as the z axis) in the caliper.
The difference is the alignment in the horizontal, front to rear, or x axis of the caliper brake pad surface. The PCCB rotor is a true 2 piece design (consumable CC friction ring mounted to a reusable aluminum hat) while the 997.2 GT3/RS steel rotor is a one piece construction (steel friction ring wedded to an aluminum non reusable hat- see below).
The alignment issue is a result of the void between the hat and the friction ring in the 997.2 GT3/RS steel rotor. With out shimming the caliper ~2.5mm away from this void the anterior (inner) brake pad surface would impinge in this area (apparently there is a Porsche service bulletin about this) while the posterior (outer) brake pad surface would be too far from the outside edge of the friction ring. Shimming out the caliper properly aligns the brake pad surface and friction ring for optimal performance.
I am not certain why the void between the friction ring and hat section exists. If I guessed it would be a function of weight savings and cooling efficiency. What ever the reason for the void it makes the alignment of the brake pad and friction ring more critical for the 997.2 GT3/RS steel rotor than for the 997.1 GT3/RS PCCB rotor (PCCB rotor has more friction ring surface area than the 997.2 GT3/RS steel rotor due mainly to this void).