Joel, you know you want it to be low riderz so it is teh best for cruizin for da honeyz!
Seriously though the only reason I can think of that would make standard springs sit the car 30mm lower is due to them sagging with age. I am assuming you have fitted standard springs that are old not new?
A short stroke shock could only bring the car lower with a standard spring if the static position of the car has the short stroke shock "topped out". To find out if this is the case just jack up the car and if the wheels don't drop at all then it's the short stroke of the shock that is decreasing your cars height. If you jack up the car and the wheels drop then it will be that your springs have "sagged" and cannot not hold the car at it's stock height.
This simple check should answer your questions.
I may however be completely wrong as I am not qualified in anything to do with automobiles