1 year later, we changed only the suspension and gained 1.1 seconds on our PB. 1.53s in the near future. Not bad for a luxury sedan with AC and radio still.

Modification List:
OS Giken Diff
ShaftWorks USA 2-way remote Coilovers 34K/26K Springs
Sikky Front & Rear Sway Bar
FIGS Engineering Parts Galore
Upgraded Radiator, Oil Cooler, and Trans Cooler
JMA Racing Carbon Fiber Vented Carbon Hood
JMA Racing Carbon Fiber Moon Roof Delete
Carbon Sideskirt Extensions
ARP GT300 Wing
Custom Front Splitter
Carbon Fiber Canards 
APEX Wheels SM-10RS 18x11" ET52 (with spacers) with 295/30-18 Bridgestone RE-71RS
CSG Spec Brake Pads - C2E Front & C21 Rear
PPE Long Tube Headers
High Flow Cats
RR Racing Tune