Hello All, if I can just chip in...
Just about to fit Eibach (Sachs) Pro Dampers and Pro kit springs (basically the standard but a bit better as Re-valved by Sachs Performance), due to my car not being raced/tracked and I'm not trying to knock seconds off my lap times so this suits my pocket and taste and I don't have to set them up!.
It's all about what you want from your car and how much money you have and want to spend on moding.
My car has high motorway mileage but I know this will improve the car and offer a slightly better than standard look and performance without giving up the comfort when on a long run - as one of you guys said the standard kit on the GTi is pretty bloody good - go too far and you forego all the millions of Euros these VW chaps spent developing the car in the first place, weight/balance/road conditions and body dynamics. If you want to go hard core then that's a different ball game and price.
I went for Eibach Pro Dampers for £180 (changing stock price) normally £450 (but look around, you can get them cheap) and Pro kit springs for £132, a good price to bring the car upto scratch and a bit more, especially if you have a few loose bushes (ooh err).
If these prices on the Pro Dampers can't be found then it's worth looking at GSF who sell all OE Sachs dampers for the GTi at £44+vat which you can match very neatly with a Pro or for a bigger drop the Sportline spring. Here's a link
http://performance-suspension.eibach.de/cms/performance_guideBe sure not to ruin your car, i've put cheap (look fancy) systems on previous cars and regretted it. If you're going to go for it then get close to KW topend ClubSport or the like or forget it, you will ruin your handling or worse. Remember also that if you go for top kit you will need a professional to set the baby up.
I would to set up my R1 Yamaha for track, road that suited me, my weight and style of riding (with professional advice) but forget 4 corners for the road and track - you gotta be a genius to do that, or more to the point you'd need a stretch of road you can run backwards and forwards all day whilst changing small increments on rebound, damping and spring rate whilst trying to give feedback through a chassis that was built for old people who want to go to the shops, laughable in motorsport terms unless you start strengthening the chassis. Bikes have chassis that are set up for racing, not Grannies and you can tell the small inputs made on rebound and damping but I would struggle to give any feedback on a standard Golf chassis over and above - that feels a bit better. You also have to then add to this what tyre you're using... bit much for someone who wants to go round a roundabout faster!
If ya car's for track mostly then, again, different ball game.
Hope this adds to the chat chaps
PS, I run a 2005 Gti car with stuff done that I've had from new and I can't sell it. Love it too much.
Bill