Cool thread I'll chime in, been using the st40 for a few years, stock gti calipers in the rear. Finding the right pad can be tedious, the tires you're using play a big factor as well. I use rs4 tires which are 200tw.
The only street pad I used with them was the stoptech sport pad, they were meh. Not a lot of bite and were just ok. I run only track pads now even when I drive it on the street.
Combos I've tried:
Carbotech xp10 front, xp10 rear
The car felt un balanced during hard braking and during trail braking on a track.
Carbotech xp10 front, xp8 rear
It was recommended by a buddy to step down to a less aggressive pad in the rear, definitely helped and the car felt good and balanced again but I felt like I wanted more bite
Carbotech xp12 front, xp10 rear
This has been the money combo for me and the car feels great. I can outbrake a lot of cars on the track and it just feels perfect. So much that I haven't wanted to try anything else, I've had about 10 sets of this pad combo and will continue. I get about double the rear pad life than I do the fronts. They're good on rotors too, I've changed the outer rings 4 times and rebuilt the pistons/seals twice. The st40 kit is awesome. Super easy to rebuild and change pads quickly, takes 2 mins each side.
