As of this posting, a decent amount of B9 RS5's are due for brake pads and rotors. Our customer found out replacing the factory rear rotors (part number 8W0-615-601-G) were retailing for $1360 CAD per side. To us that is beyond ridiculous!
We looked no further to recommend Girodisc as replacements (part number A2-149) as they offer a lighter (unsprung weight shaved), better ventilated, and more durable setup. To top things off, Girodisc rotors can be serviced by reusing the hats and only replacing the rotor rings when they are due. All of these features and the cost was only about $1350 CAD for the pair, making this option the best for RS5 owners in both performance and price aspects.