Gladly.
Well, first I recommend going through some of articles from StopTech, they are excellent reads.
Resource Library
Here is a good one to start with https://www.apcautotech.com/getmedi...e-Systems-and-Upgrade-Selections_8-2018_1.pdf
Now, StopTech argues, and I agree with this, its important to maintain balance when it comes to brakes. Which means you don't want to increase stopping force only in the front or the back. So for me I wanted the brakes to last longer on the track and the 13/14 brakes kit do just that by increasing the rotor diameter and the pads surface area without increasing stopping force.
How do I know all of this, from one of the StopTech articles, they give you the formula for the torque generated at the wheel and its basically a multiplication of 1.fluid pressure 2.caliper piston area 3.friction coefficient from the pad 4.diameter of brake rotor.
After digging around, I found the piston area of the Brembo 4 pot to be 4.3 in^2, and the 13/14 Brembo 6 pot is 4.26 in^2. If you do the calculation you'll find the 13/14 is only %6 more torque, its probably less because the whole system is not %100 efficient. Loss in pressure or deflection of the caliper will effect the final results.
The 15+ caliper and the GT350 are 4.73 and 4.75 in^2 respectively and they are IMO too much for our cars, unless one can balance the rear with the fronts I wouldn't touch them. Besides, based on hydraulics you'll see that the larger piston area would make the brake pedal travels longer and probably feel softer. But for the 13/14, the smaller area will make the pedal firmer, but again I don't think it will be noticeable.
I dont see how your post proves anything about not improving braking power.
Also you do realize that the 15+ 6piston uses basically the same size rear as the 13/14 gt500.
Yes brakes need a balance. But take the gt350 brakes for example. They have extremely well set up brakes over the performance pack 6piston setup on the gt. Care to explain that?
Imo there is no such thing as too much brakes.