The Cayenne stuff has a total piston surface area of around 56cm through to about 60cm - being honest its not a great pedal, the ideal total piston area is around 49-50 sq cm. You'll find with 6 pots with this piston surface areas that the pistons are split normally 27/31/36 or thereabouts. Even the smallest Q7 caliper is 30/34/38 might not sound like a lot but when you start multiplying the radius by its self and then by 3.142 you get huge volume that the 23.8mm master cylinder on the mk5 just cant push.....
They look rather good though
With no seal drag with pressure applied the smallest piston will deploy first, so you can "tune" calipers to feel better, they normally mess around with the smallest piston size to make brakes feel sharp, the bigger pistons will start to apply pressure when the smallest piston has reached the limit of its travel which is normally about 1mm.
Porsche 996TT calipers have a big piston split at 36/44mm but work very well, 38/42mm splits are also good (Ferrari 360/R8 Rear) works. 36/40mm works well on a smaller disc.
Personally the only 6 pots I would fit to my car would be AP CP5555's or CP7041 or Carrera GT rears or GT3 RS fronts, unless you want to blow over 1500 quid on brakes.
Regarding the R500 disc it is what it is, you need some mass to absorb the heat generated - no heat/no braking, even two piece 340-360mm assemblies weigh much more than stock, if you
need big brakes its normally because you have a powerful car so corner entry speeds will be higher so you've got a lot of energy to get rid off. Dont forget the potential energy that needs dissipating is proportional to your speed squared so that if you can get to your braking point at 80mph instead of 90mph then its not just another 10mph (12%) you need to get rid off its about 25% more energy.
You pays your money I guess
