Rotor size is but one piece of the puzzle when it comes to braking ability.
Just because a car has 12.8 inch rotors means little in terms of direct braking torque, unless you're able to factor all the other pieces into the puzzle (piston area, MC piston size, pedal ratio, hydraulic pressure and clamping force).
Also, pad material has a big impact on braking torque as well, and pedal feel to a large extent.
I always get a kick out of people who want to compare numbers vs numbers on a car. This is like saying a car with a better skidpad number is automatically a better handling car than one with a lower number. Skidpad number reflect one thing...ability to grip around a skidpad. It actually has minimal impact in the reality of *handling*.
The Supra's are a nice car, but wildly over-priced in my opinion. They've held their value well, especially compared to the 300ZX's and RX7's of the Japanese competition.
However, they have never been a popular road-racing car, in part due to the overall weight of the vehicle, and probably due to the cost. Probably not a bad investment to buy one as a collector's car, but I wouldn't want to buy one as a track car.
I've known a lot of people who run the Supra as a 1/4 mile car, but nobody who runs them as a track car.
Oh, and Jon, you might *think* one would handle better than the other, or be quicker in the 1/4 mile, but we know you haven't driven either one. So you're *guessing*, rather than thinking....aren't you?