I have upgraded to 996 GT3 PCCB front on my turbo few months ago, and the same seller is putting the rear calipers for sell in a reasonable price too. I was planning to get the caliper spacers on the rear anyway, for upgrading to 350mm discs(997 turbo rear steel are on its way).

But then I actually find the GT3 PCCB rear calipers is using the same brake pads as the turbo rear calipers, so, the only benefit would be the up-size disc(Same as spacers) and the shape, am I right? Thanks

 

The 6GT3 calipers have longer standoffs and are designed for a 350 rotors. You don't need a spacer with them..

 

Thanks, I knew that and thats my question, replace it or add spacers.