I have a set of prodrives in my 04 sti and drive the car in Long Island as a daily driver,I prefer the drop vs the pinks and felt the pinks would be too harsh. I recently helped a friend install his pinks and then did some testing. The spring rates felt slightly higher with the pinks and more linear. The prodrives are a progressive spring and absorb road imperfections better than the pinks. Both cars had hotchkis front and rear sways,steering rack bushings.
I would say if you drive mostly on the street go with the prodrives or if you drive mostly on the track or track conditions go with the pinks. I previously owned an S2000 and loved the handeling as long as the roads were smooth,but hit a bump in a high speed sweeping turn and look out,skip and hold on! I just didnt want those characteristics in my next car.
As for the grpn hats ,I never swapped mine but my buddy did with his pinks. The prodrives definately smoothen out the ride,less bobble headding. So experiment like me. After the prodrives I think I'll try a set of whiteling G4's.