Finally got the GM Performance struts and shocks installed.
They are essentially the RS struts and shocks, but made a bit shorter.
The car is somewhat better damped now, with an ever so slightly more sporty ride, with a little more road feel generally. Although it is subtle, not at all night-and-day from the stock dampers. There is just a slight difference in overall feel, not anything you can really put your finger on. It just feels solid and competent. Have only driven it a couple of days though.
One note: I think these struts may compensate for the camber change of lowering springs. The front camber changed like .05 (in the right direction) compared to lowering springs with stock struts.
With these dampers and Eibach springs, my car is riding like an RS, but an inch lower and with a better highway ride due to the Eibachs and proper touring tires.
I am quite happy with the setup, but can't help wondering what the ZZP rear sway bar would be like.