I know this is an old thread but I just tracked these this week with Raybestos ST-43 up front and Powerstop Track Day spec on the rears. I think I either bed these in wrong or am using the wrong fluid but after about half way in my first session, I must have overheated something because I got pretty bad front vibrations only during braking for the rest of my two HPDE days, got better as the days went on but still very noticeable. Also got some brake fade at end of sessions with ATE200 fluid, RS3 deflectors and heavily trimmed dust shields. I use Powerstop Z26 on the same rotors for the street and think my issue is not using a dedicated rotor set so the existing material is probably screwing up the race pad.
As far as the initial pedal feel of the calipers, after first install and bleed it was pretty loose but then driving them on the street for 2 weeks and doing another power bleed, pedal feels firm along with the typical OBD11 tweaks. No RRG or RPV used, just SS lines and the Zimmerman blanks. On track, the pedal was firm for the 1/2 half of sessions and bite was almost immediate.
From a track perspective coming from PP brakes and Ferodo DS2500, these definitely had the bite I'm looking for but with the heavy front vibrations and stuff it still isn't confidence inspiring. Not sure if getting 2-piece rotors and/or Motul 660 fluid would help in those regards from a cooling perspective. Most likely I'll just get new front rotors dedicated to the Raybestos and bed them in again very specifically to spec as this is now hindering consistent lap times at the track and just want a solid/stable brake experience.
The soft pedal was almost 100% likely cause by fluid boiling.
The vibration was overheating the pads and getting deposits on the rotors.
If your going to swap pads and use same rotor, you really need to use pads with similar materials used. You can't use a ceramic pad on street, then just swap to a semi metallic track pad on the same rotors.