KTS questions

[4thHorse]

Hey guys, I have a few questions so I did some reading and think I found the answer. If you guys can tell me if I heading in the right direction that would be great.

I bought a used 240sx 96 that has KTS coilovers and it was alittle to low and harsh. I raised it up alittle and changed the damping. My problem now seems to be that the rear still seems to harsh. The damping before was 10 in front and 5 in the rear. Now its at 5 in the front and 3 in the rear. when I was raising the rear I think I might have added to much spring load to the spring, so can this be the reason for the stiff rear. Should I have lengthen the coilover assembly instead of at the spring perch? I've read that KTS can be harsh, but the front seems to be pretty forgiving now. So the question is am I on the right track? More info on the car if it helps.

18x8.5 30 offset 215/40/18 fronts need to be replaced thinking of going 235/40 your opinions would be great.
18x9.5 12 offset 235/40/18 rears good shape.

Both fronts and rears are streched, can this also account for the ride. I would like to drive with some comfort at the same time rip things up when I need too.
Any help would be great.