well i was just informed by a tech at Tire Rack that if I went with a 19" rear and 18" front, then my handling will be worse. I told him that a lot of the supercars have staggered diameter as well as a lot of Foose's custom cars. He said to just stick with the 18's all around and gave me a price of $3900 which includes 4 Michelin Pilot PS2's with a 265/35/18 front and 315/30/18 rear.
He said that all of these other "supercars" had staggered diameter and also different size front and rear wheel height. He said the Mustang was not designed for staggered wheel height. I am still not sold on what this guy is telling me.