I have spent quite a lot of time researching old posts and making calls to
suspension vendors in the quest to figuring out what
suspension package to buy, so I hope I can help you with the info that I have gleaned…
Eibach Pro Kit Plus- Includes springs, struts, and antisway bars. The sprins and sway bars are quality pieces. However, some say that sway bars should be pretty far down the list on planned
suspension mods. They say that (A) beefier sway bars can make for an unnecessarily less comfortable ride and that (B) you should optimize a lot of other
suspension pieces before worrying about the gains to be had from bigger antisway bars. One fellow claimed that the dampners included in the Eibach kit are not of good quality, that they are oil filled rather than gas filled. He claimed that oil filled dampners are much more prone to fatigue and failure in high performance driving. I must admit that htis was only one man's opinion, but he seemed to know what he was talking about with
suspension mods.
Engineered Performance 2005-2006 Mustang GT Performance Pack
The springs, lower chassis brace, adjustable
lower control arms, third link, and
panhard bars all seem to be good ideas for increased traction, but not all may not be necessary to achieve the results that you desire. The jacking rails are useless on a non-competition car. Unless I am grossly mistaken on what these are (I am thinking of a tubular steel element allowing you to jack your car at any point along the unibody), they are pointless. They may achieve a subframe-connector like effect, but many doubt the necessity of subframe connectors due to the chassis's stock rigidity. Dead pedal sounds nice, but there are probably cheaper ways of putting one in your car.
FRPP-
The Multimatic dampners are said to be of high quality, but overly stiff, even for the increased rates of lowering springs.
Personally, I would make my own "package" with the following components:
1. H&R, Eibach, or Steeda lowering springs. Choosing a spring just depends on the drop that you want.
2. Adjustable
panhard bar and
panhard bar brace. These components will help to more positively locate the rear axle in hard cornering.
3. G-Trac (or lower front control arm brace) from Steeda or BMR Fabrication. Ties together front
control arms so that geometry is maintained under high loads.
4. Keep the stock struts or upgrade to the adjustable Tokicos when they come off of backorder. Eibach says that their pro kit springs will work with the stock struts. Also, my boss (I work for Latemodel Restoration Supply- a really big 79+ Mustang aftermarket dealer) said that for my purposes I would be more than satisified with stock struts and some new springs.