SS any model springs will drop and LS or base G5 about 1 to 1.5 inches
Eibach prokit will do nothing for an SS, SS/SC, or SS/TC. LS 1 to 1.5 inches
Eibach sportlines is agressive drop but ride is harsh and pogos on ruff roads. (Even with Koni shocks) SS 2" drop LS 3" drop
THere are other brands: B&G, H&R, Progress, SSC, ARK, Sport Tech, and there are more.
I have Progress Springs drop is just slightly less than sportlines by half an inch but ride is superior to sportlines.
For basis purposes I have Progress springs with Koni adjustable shocks and TTR rear sway bar. 17" G5GT wheels with 205-50-17 Cooper Zeon Sport A/S tires
These are my results of trial on the different springs that I have tried or installed for someone else with a cobalt or G5. I have run SS/SC springs, Eibach Pro-kit, Eibach sportlines, and Progress
Your results may vary.
But I personally love my Progress springs with my Koni Shocks and TTR rear sway bar. Good ride and Great handling.