No experience with the eibach ones but can say my set up certainly did stiffen the chasis and sharpen up the steering. I still have my old front and rear ARB's if your interested. As you dont have the sport set up I understand that the front will be approx 3mm thicker than what you have as my OEM one is exactly the same as the S4's and I think my OEM rear is 1/2 mm thicker. Can easily check the thicknesses for you if you want.
I am not sure about prices for the eibach kit but I ended up paying around £500 for my H&R front and Neuspeed rear. So if you are intersted in mine you could have a cheap upgrade at £100 for the both.
Just one last thing to note. Even though my car does handle much better with the ARB's they have made the car so stiff that I has taken almost all feel out of the steering wheel and although it corners extremely well it doesnt actualy feel that fast & hense can kill some of the fun.
Its a long story and I have still got a few issues to sort out with it. However the perfomance figures are off AmD's rollers. To be honest I am not 100% confident that they are accurate and think they maybe a little over. My car only boosts to 1.0 bar and other tunners like Jabba say they can only get 230 ish from 1.2 bar hense the reason I am a little sceptical. However AWE & a few other american tunning sites claim 230 @ 1.0 bar for a K04 so perhaps my figures might not be too far off. Until i get it run on a different dyno I wont really know. BTW when you going to get yourself a boost gauge? Cos you really should get one as a diagnostic tool as you have spent so much on tunning your car. I would be interested in hearing what type of boost figures your getting.
Funny you should say that mate im buying one today a digital one here is a little piccy it does both boost pressure in PSI and Charge Temp which i think is a good gimic. And to see how well my FMIC cools the air.