Updated info. I called over to the shop on Thursday morning to discuss a couple of things. I was planning to go down there and take the measurements. Unfortunately, they already had the car up on the rack with the Brabus (OEM Eibach Sportline) springs removed in anticipation of installing the Eibach ProKit springs. So I wasn't able to re-measure.

The Eibach ProKit springs arrived and have been installed. Yesterday evening I went to the shop and drove the car with them, and I liked it because it's a bit softer still than the Brabus (OEM Eibach Sportline) springs. If I had to make a seat of the pants guess, I'd say that the Eibach Sportline springs soften it up by about 2/3's what the Eibach ProKit springs do. Incidentally the guys at the shop who drove it both ways all agree that it's a bit softer with the ProKit springs. Either spring kit is a noteworthy improvement for street driving, at least if you've got bumps in your roads and want a more comfortable ride for your date, and your own rear.

When testing both times I drove it a bit aggressively around some streets and some fast curves. Obviously I couldn't go that fast, etc., but I'd say if you're into racing and driving a performance car, you might want to consider using the Sportline Springs, which aren't as loose as the ProKit Springs and might be a great compromise for some of you. The other alternative is to keep the originals for racing, and the ProKits for street, and switch them back and forth as needed.

Note that all of this testing was done with the Brabus (OEM Bilstein) shocks installed. Since the shocks and springs were done at the same time it's a bit difficult to assess each individual piece, but the damping and rebound are improved without doubt and the severity of jarring when driving over bumps, in which both springs and shock are involved, is much improved. The Bilsteins are a good change.

As for the drop, visually the drop of the ProKit Eibach's is similar to the drop of the Sportline Eibachs, though maybe just a bit less drop in front, and a bit more drop in the rear. To my eye this is going the correct direction. I'm hoping it drops a bit more in the rear, but we're planning the put a thicker spring pad in the front to lessen the front drop a bit. Also, there may be a tad of rubbing while in reverse one of the front tires.

I'll post photos and take some measurements when we're done.

Eric