Looks like we have pics of both the V6 and v8 prototypes. Notice how they cleverly hid the exhaust tips as much as possible on them. The two prototypes parked next to the blue Mustang convertible look like the V8s and the solo shot prototypes look like they have 17 inch rims on them which I guess are the V6 models.
The V8 models look fantastic with those rims IMO, and fill out the the huge wheel wells very nicely with the 19-20 inch rims. If they are also developing the top dog at the same time, I'm guessing the car with the dark finish, gun metal rims right next to the blue 'stang is our top tog, and the one next to it is the regular V8. The V6 models could use bigger rubber though.