I can tell you what not to do. Don't get 18" wheels, Eibach pro kit springs and koni FSD's, you'll find it takes corners like a train on rails, but it's a far cry from sitting in an E class merc.
My advice - if you aren't bothered about lowering the GT, use standard springs and put some Bilstein B6 dampers on. I've no experience of that combo, it's just a guess. Unfortunately for me I like the look of my GT as it is (lowered 25ish mm and with 18" wheels) too much. I know I should go standard springs and 17" wheels to get the ride comfort I want.
Good luck, let us know what you end up doing.
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.