Initial Impressions
Upon opening the Eibach box, I was not surprised to find the springs were of usual Eibach quality, that is, the springs looked top-notch. After speaking to the rep at Eibach, here is what they changed from the 4Gen Pro-Kits (4016.140) to the 5Gen Pro-Kits (4035.140): the free lengths are longer, this was to help the extreme lowering that 5Gen Preludes got with the 4Gen spring kit, the fronts are slightly (4 lbs/in) softer, and the rear springs are more progressive (i.e. they actually start off softer, but increase in stiffness considerably faster).

Installation Impressions
At the time, I had Tanabe Super H springs installed on my Prelude, so I was anxious to compare the two sets. When I removed the Tanabes, I took a few pictures of the springs side by side, along with the stock springs. Here are the fronts:

The stock spring is on the far left with the Tanabe Super H spring in the middle, and finally, the Eibach Pro-Kit spring on the far right. Note that the Eibach spring looks slightly longer. Here are the rears:

Here, the stock spring is on the far right, Tanabe in the middle, and the Eibach on the far left. Note that the Eibach again looks slightly longer, but it is much more progressive than the Tanabe. Installation was a snap, and there were no surprises.

Performance Impressions
The new Pro-Kits (4035.140) are visibly different than the 4Gen Pro-Kits (4016.140). On Todd's Prelude with the 4Gen Pro-Kits, there was almost no rear fender gap and about a 2 finger gap on front fender. With the new Eibachs, I had a little less than a 2 finger gap on the rear, and about a 2 - 2 1/2 finger gap on the front. Visibly, it looks like the rear is lower, but the car is actually level. Since the rear fender is cut differently, it looks like it is lower. I was surprised that the Eibachs actually felt stiffer than the Tanabes. I thought that the Eibachs might be softer since the free length of the Eibachs was longer, but the Eibachs still lowered the car more. The rear springs were absolutely more progressive than the Tanabes, and the springs really helped to stiffen up the front and rear end of the car. Unfortunately, a side effect of stiffening up the front or rear suspension (with springs, dampers, bushings, or strut bars) is that the sunroof rattles like hell now over large bumps or a series of bumps. I guess the chassis has to flex somewhere, and the sunroof is the weak spot. Performance wise, these springs are absolutely worth the money. I had to opportunity to take the car to an autocross down at Texas A&M with the freshly installed Eibachs (they were only installed for 2 days when we went down there). Overall, I was very impressed. Body roll was reduced, as was dive and squat. The bounciness associated with using stock dampers with aftermarket springs is almost nonexistent. There is a very slight bounce on very large bumps, but over the small road imperfections, the car keeps its composure extremely well. The only drawback to the Eibachs is that they lower about 1 1/2 inches, so there are some concerns with negative camber (which for autocrossing, is good!). I took the car to my dealer to have the alignment checked, and it came back that the front camber is about -1.4 degrees and the rear is -1 degree. Not bad, but I have been thinking about getting a rear camber kit so that I can rotate the tires for even wear. I really doubt that anyone will develop a front camber kit, unless they offer a rebuilt upper control arm. If you take off the front tire and look at the mounting for the front upper control arm, you will see what I mean. Otherwise, I haven't had any problems whatsoever with the springs, and I am 100% happy with them. Also, for those of you with Power Extreme exhausts, I have not scraped on anything yet, but my friends that have followed me say that the PE gets REALLY close to scraping on some speed bumps, driveways, and dips in the roads. If your main concerns are performance and you plan on autocrossing with the stock dampers or perhaps some Konis, give the Eibachs a serious look. I highly recommend them.