If the final car has the dimensions of the show car, I think it is safe to assume 17 or 18 rims. Whatever the rims are that are on the new GTO or the Holden are probably the size they will be using.
Most people don't know this, but when a car has 18" rims, they have to soften the suspension to compensate so your rims don't get so easily bent when you hit a pothole. They do this on the new mustang GT if it's ordered with 18" rims. It has a different suspension.
I am also pretty sure the suspension is softer on dodge trucks that come factory with 20" rims based on how it felt when I drove one.