Re: wk eibach vs h&r lowering springs.
Dont know. You need to do your research and get the spring rate of the stock springs, the Eibach and H&R, and the SRT8 springs. How much does a WK SRT8 weigh? How much does your WK weigh? I would also replace the shocks f&r with Bilsteins? Talk to Bilstein before you buy about your springs etc. I would replace all the bushings etc. Might also look at Fox shocks.
What are you looking for out of these changes? How often do you go off road?
Do you just want to lower your GC?
Why are you making these changes?
Just dumping in SRT8 springs may not be the best option since they maybe shorter which would require different shocks and struts(?) to work correctly.