On the picture above, the length of the red threaded section is the amount of height adjustment you will have. Though it is not all usable; the amount you can adjust the height depends on the amount of travel the shock absorber has.
For example, if you were to install these in your car, and the springs compressed 50mm under the weight of the car, you just lost 50mm in which the suspension can compress before the shock bottoms out, but gained 50mm in which the suspension can extend before the shock absorber is at full extension.
Now if you can imagine the coilovers in the picture above but with a 50mm shorter spring due to the weight of the car, you would probably have the ability to lower the car(by the amount of threaded sleeve that is under the gold spring perch) by more than the distance the shock absorber can compress, and thus your suspension no longer has the ability to compress as the shock would be bottoming out.
I guess what I'm getting at here is, the more you lower the spring perch(to lower the car), the more suspension travel you lose in the way of compression. The more you raise the spring perch, the more suspension travel you lose in the way of extension. So the spring perch may offer a large range of height adjustment, but all that adjustment is no good if the shock absorber cannot function in parts of that range.
So the amount of adjustment you have will depend on how the coilovers were made: the length and travel of the shock absorber, where the threaded sleeve was welded onto the strut tube, the length and rate of the spring etc. It's hard to say without seeing the coilovers or knowing the dimensions. I'd estimate around 3 or 4 inches height adjustment that will still provide sufficient suspension travel??
Edit: does that even make sense? :blinks: