For sure, Terry Fair of Vorshlag would weigh in on the side of larger rear brakes for the Mustang (or any front engine car with an anywhere near similar difference in rotor size).
http://www.vorshlag.com/index.php?cPath=141_142_280
http://www.vorshlag.com/product_info...roducts_id=606
He and his wife have been running a street-legal and air conditioned 2011 GT variously in TT3 this past year (and SCCA E-Street Prepared during 2012), with considerable success.
http://www.vorshlag.com/blog/
I have to agree at least generally with the notion of rear rotors of more equal size relative to the fronts, at least as long as you can stay out of brake hop (something that some years of the stick-axle Camaros/Firebirds were very sensitive to). Basically, it's foolish to have to throw away any rear braking as a Band-Aid for some other brake-related shortcoming.
And just because I think Camaro5 members will find it interesting, Vorshlag is also known for developing kits for swapping LS-series engines into BMWs . . .
Norm