One thing you might consider doing now is switching to r-comps. Lots of little adjustments needed when you switch and if you are at the level of playing with valving and spring rates then it seems a wasted effort to do so on street tires only to redo everything again once on a proper track tire.
Removing the rear sway seems a blunt way to fix a problem that's likely not solely related. When are you getting the sudden loss of grip? Spring rates and high or low speed valve adj are usually the best avenue of adjustment. Possibly initial static alignment could be an issue too? Changing out factory bushings may help as well. Another source of information would be the M3 track guys; dynamically a bit different but still very similar geometry and hardware. I'm just spit balling here but let us know what you end up with!