Cheers CS, I had a bad experience with Prokit springs and Bilstein B6 or B8 on my old 156 SW, they didn't really hold the back end up! Nice and level, but even with my 9 and 10 year old in the back they would bottom out, with any decent weight in the boot they would literally bang (they were defo the correct spec). I put some GT V6 springs on and then it never bottomed out (little bit higher too). Having said that, I have Prokits and fsd's on my GT V6 and even with a totally loaded with people and kit, it never bottoms out.
GT 3.2 V6 - Q2, KONI FSD & EIBACH PROKIT, GTA REMAP, MICHELLIN PS3's, BMC CDA
159 SW 2.4JTDM TI - ALFATUNED, WIZARD BACK BOXES, KW V3 COILOVERS, NOKIAN WR A3/MICHELLIN PS3, PCA DYNAMICS ALIGNMENT.