I will agree that the stock Pantera pads need to heat up but what I see is one or two touches of the pedal and they are ready.
I have the Porterfields on both my GT350 and Pantera. The Shelby was first. The first thing that I noticed was the hardness of the Porterfield with the first touch. It was like the pads were wet.
Two touches and there was a response. The first touch was one of those "come to God moments" where your entire life flashes before you in an instant and the beads of sweat are instanly there on your forehead.
In what I am seeing, that is VERY similar to how the stock Pantera pads work.
I apparently was taught that you get underway gradually in any vehicle and the first thing that you do then is test the brakes. Truckers do this religiously.
Scientifically I'd need to do a controlled experiment of measuring the stopping distances with one v the other and that is simply not worth the effort unless I am the manufacturer and want to emphasize the positives.
Where the Porterfields shine is when the brakes are smoking hot.
...and they do smoke when hot. 
Incidentally, the point of using the 1.25" wide vented rotors v the .710 either vented or solid, is that the cooling vents are more significant and they cool faster under extreme conditions. The solid rotors of course have no cooling vents at all.
Originally the Comp Cobras and the GT40's all used solid rotors which I always found interesting since ultimately one of the difficulties in them was early brake failure under competition conditions.
This became such an issue that eventually the Mk.IV's had wheels designed for them with fan blades as part of the wheel spokes. Each wheel location had a unique wheel for it which blew air out of the wheel well. The intake was supplied by 4" ducting from the nose of the car.
Solid rotors are something very consistent with European originated cars. I'm not sure Girling approved at all of vented rotors?