Thought I'd give an update - it's been a while.
Spoke with a few performance shops and the first thing each said was "Coil Overs" and lower the centre of gravity.
Looking around, like everything else, you can thousands for a kit and hundreds more for installation and the very necessary alignment.
In the end, I opted for the Pedders SportsRyder eXtreme XA Adjustable Coilover Shock Absorber Kit - supplied and installed for $2.5K (I'm sure the price has gone up a bit since).
I'm not looking for track performance, just good, predictable street driving.
As these are height adjustable, I requested a 25 - 30 mm drop. Lower, fill the wheel arches but don't go OTT.
My first impression is that the car is flatter (25mm drop front, 30 mm drop rear).
It's a little bumpier - but only on the bigger bumps - hardly noticeable on regular roads.
Braking is flatter, cornering flatter and tighter and off the line seems to have improved too.
Service out of Pedders Burwood was great - and they offered a check up after the first month.
Car looks better too - much better stance.
Overall I am very happy with the result and would recommend this set if anyone is just looking to get the bit better performance out of their standard S550.
Anyone else fitted this set ? what do you think ?