If you just want slotted only I'd just go with the Girodisk rotors (cost wise)... which I plan on doing after I have 19's on. Brembo makes a slotted only 380mm rotor as well.. but it's $$$$

http://www.girodisc.com/Girodisc-Fro...S6_p_6543.html

If you don't want to upgrade the wheels the ECS tuning RS5 rotors are now an option... Maybe they'll make just slotted for stock sizing as well??

http://www.ecstuning.com/Audi-B8_RS5...ors/ES2785596/

http://www.ecstuning.com/Audi-B8_RS5...ors/ES2603007/

We share the same Rotor offsets as the 2013-2014 RS5, The gallardo's and the R8's.