Recently put the yellow springs on my 2006 STi and finally had a couple track days on them. Used them for two days on NJMP's Lightning course.
These are the best aftermarket replacement springs I have installed on any car ever!
The result is truly as claimed in the advertising. With significantly higher spring rates yet fully within the dampening control of the OEM struts.
I have ground control camber/caster plates which do lower ride height some - if I was on zero height change top mounts the ride height would be perfect. Even with the lower plates the ride height works with wider tires.
Combined with larger sway bars (I am using Whiteline 24mm adjustable front & Whiteline 22mm adjustable rear on stiffest settings) the handling improvement over stock is incredible. I am able to turn in at considerable higher speeds and carry those higher speeds through the track out. On my stock springs I had to run the rear sway bar at its softest setting (tire lift), but am able to run them at their stiffest setting now.