^^^^ you won't get an exact drop as they are springs, every case (within reason) will be different. Look on the manufactures websites, usually give you a distance BETWEEN which the springs will drop you car or will say UP TO said drop.
Chap I know on here had H&R's on his Eddy (albeit with spacers fitted to his wheels to clear his BBK) and it dropped the front end around 40mm so the edge of the tyre was exactly in line with the ach, looked the dingles and fine in a straight line, give it some spirited driving around a corner and rubbing occurred. Another chap ran the Eibach Pro's and got NOTHING at all, no drop.
Adjustable coilovers is your answer or H&R Springs.
Check out GNJ Motorsport's site for springs. Speak to Graeme, he's also a member on here.......
~~ Clicky here ~~