IMO, unless your world has roads as smooth as glass and there are no inclines or driveways, speedbumps, etc., the Eibach's and HR's will be as low as you want to go.
This is especially true if you go to an aftermarket exhaust. Going too low just kills the handling of the car as well.
Just looking at my stock ride height................I didn't think that the H&R's would drop it that low. They advertize a 1.6" drop. By looking at my car you'd figure you'd need at least 2 - 2 1/2" drop for that stance.