The Ford Racing SVT GT500 19x9" Front wheels are 40mm, and the Ford Racing Boss 302 19x9" Front wheels are 42mm, while the RTR 19x9.5 are 33mm.
In my opinion, the RTR wheels stick out too far in the rear at 33mm on a 9.5" wide wheel. If the wheels your looking at have a 35mm offset at 9" wide, they will tuck in about .2" closer to the car. Run with a narrower tire like a 255, they should sit about as flush as you can get with looking strange from the 4-5 or 7-8 o'clock view.
2015 Mustang GT PP 401A Black | Roush Supercharger