One of my favorite past times is weighing parts and seeing if saving can be made with minimal compromise(each to there own =P) As most would know weight saving can be one of the best performance upgrades.
As I've found with the C43 there is very few lite weight parts if any,though it looks like they did attempt it on the brake rotors.
The stock 334mm C43(210/208) rotors are a two-piece with alloy hat,there a nice looking rotor especially with the cast AMG logo.
For comparison I have a 332mm stoptech kit lying around, the rotor are the same thickness as the AMG however the depth of the contact surface on the AMG pad to rotor is much more.
Results:
AMG 2-pot cast Iron Caliper w/pads 8.5kg(18.7lbs),(Pads ~0.7kg each)
AMG Rotor w/slight wear 9.65kg(21.23lbs) (would be closer to 10kg when new)
Stoptech 4-pot Alloy Caliper w/pads 5.25kg(11.55lbs)(pads 0.5kg ea)
Stoptech Rotor new 7.65kg(16.83lbs)
To summarise, The AMG brakes weigh 5.6kg(12.32lbs) more per side than the Stoptech's, - thats a fair amount!
Imo the greatest benefit would be in the lighter stoptech rotors due to the rolling mass,with secondary benefit being the un-sprung reduction ,One compromise is the Stoptech tend to squeal when cold. As far as life of the rotor I would imagine the stoptech rotors wouldn't last as long as the AMG's Larger contact surface and pads but I could be wrong.
Would I swap out the AMG for stoptech's? Tempting in most aspects!.