[88carrera]

Nice car!
I ran into a problem with extreme inner rear tire wear using H&R "Sport" springs on my 2003 C2 (not a turbo, of course). First are the positives: 1) The car is lowered ca. 1.25 ", which is about the same ride height as a GT3. 2) The car looks great at this ride height. 3) The car handles extremely well both on the street and on the track in this configuration. 4) The ride is firm, but not too harsh in my opinion.
Now the negative: The lowering makes it impossible to set the rear alignment within factory specs because it is not possible to have enough adjustment to reduce the excessive negative camber that causes the inner tire wear.
Here is the solution that I chose: I installed adjustable upper rear control arms in place of the non-adjustable OEM "dogbones". These adjustable upper rear control arms are available from several aftermarket suppliers. I got mine on E-bay for ca.$400. According to the Porsche PET (digital parts manual), the rear suspensions of the 996t and the 996 Carrera 2 have exactly the same upper rear control arms, so my solution could be your solution.
My car no longer has any excessive inner tire wear in the rear and tracks perfectly.
Hope this helps.