OME springs aren't designed to lift the vehicle per se, but rather to improve it's load carrying capacity, so you select a spring based on the intended load - all of the springs are intended to provide the same lift, approximately 30mm.
For the front you have a choice of stock +75 lbs, or stock +75~150 lbs, and for the rear, you have a choice of stock +light (upto 300lbs), or stock +medium (400~700lbs).
There's an application chart on the ARB website that explains this.