Here is a pic of the 11.4" rear rotors installed
and a pic of the 11.3" stock front rotors.
Stock rear rotor size is 10.3", so you gain 1.1" in diameter. The rear brake pads are just over 1.3" tall at their widest, meaning swept area on a 10.3" rotor is about 19.7 square inches. Swept area on a 11.4" rotor w/1.3" tall pad is about 21.95 square inches.
So with 11.4" rear rotors, you'll have 111% of your original 10.3" rear rotor braking power.
I noticed that the back end "hunkered down" a bit more under heavy braking. Worth the time and money, IMHO. FWIW, I'm using Porterfield carbon kevlar pads.