I've got ProStars on my '03 GT. I'm running 15X10's out back, with 6.5" of backspacing. Up front I've got 15X5's, which only come in one backspacing. You'll need a 7/16" spacer (Mr. Gasket makes them) for the front wheels. Many folks recommend changing out the front studs to long ones for safety sake, but, knock on wood, I've never had a problem. For tires, I run 205/70/15's on the front, and 295/50/15's on the rear.
You can run 15X8's out back also, with 5.5" backspacing. Some folks like the 15X3's up front, but I'm not a fan of running these on the street when you have to do freeway-speed driving. Also, if the diameter of the front and rear tires is way, way off, it can trigger the ABS light if you have it.
Jerry
