It depends on what you're doing. It's probably not a difference you're going to notice driving around town. Honestly, one of the reasons that I did it was to lower the rear of the car. Because of the way I did the brackets, the car sits about 3/8" lower.
Hopefully I'll get them installed relatively soon. I'll try to do a write up on the installation with before and after pictures.
As for the sliders, the idea is two-fold. Shackles force the spring to travel in an arc, which doesn't necessarily track the movement of the suspension. The other is that the shackle bushings provide more than a little resistance to the movement of the spring, so, binding. The idea of the slider is that the spring eye moves with almost no resistance, and moves in a linear fashion, which is what the spring wants to do anyway. So, the spring reacts faster and without binding and the suspension works better.
Ideally, the slider would be mounted at a slight angle so the spring movement would track properly. The AFCO's don't really provide for that unless you build it into the mount. Calvert makes a set that has the angle built in, so you can mount the slider flat. These are the Calvert's, you can see the small angle on the track. I didn't find out about the Calvert's until after I had bought and installed the AFCO's.
