I just installed the GC sleeve kit on my car (430lb front and 650lb) rear and hit the track yesterday. I am a decent driver (instructor for a few local track day groups) and have had some seat time in dialed in cars, and I must say that for $1,000 this kit is freaking awesome!!!!!
I ran the car with 275/35/18 NT01's squared and it was totally predictable and handled low speed and high speed bumps very well.
I have never been this happy with a budget suspension setup and have no regrets with this kit.
Edit: Regarding the KW kit, that's just for style points, if you're looking for performance go with the GC or TCK. For GC vs TCK, the TCK kit looks a little fancier, but at $375 more, I would stick with the GC kit.