What rear ride height are you running?I don´t have any feedback of Teins, but I am running 7kg front and 5kg rear springs. The rear springs are too soft for track use. I am changing them to 6kg and try from there next summer. I also have a adjustable rear swaybar and damping, but I can feel the rear springs are not adequate on higher compression. I am still on street tyres and when I get better gripping tyres I also need the rear to be a bit stiffer.
Do you mean @2pot to put 40kg in the boot if the tank is empty? My tank was full when leveling.Put 40kg in the boot to simulate a full tank, then lift to 340mm - it'll roll less at the rear.
What rear bar and rear alignment?