i think i may have lifted it from an american Ducati site, cant remember to be honest!--dont forget if you are upgrading to a twin disc you may have to upgrade the master cylinder too
there are differences between the "gold-line" calipers and the P4 (4 padd'ers) - i.e larger swept area etc etc
The R's are the main culprits here - as well as a 15mm offset (instead of 10mm) they have the narrow-band type discs fitted and the older larger swept are discs will not work without modifying the brake pads - not recommended IMHO
There are also different materials used - cast iron and SS etc etc
no quite so simple when you look into it - but a good guide nonetheless