3 weeks ago I upgraded my 05 GT wagon with billies from wheelpower + a set of STI pinks and am very hapy with the result. The original suspension had about 160,000kms on it, the front was ok but the rears were completely shot (sagging badly and had very poor dampening, handling was really bad particulaly when weight shifted changing direction).
Initially Eibachs were recommended to me but neither I or my mechanic could get hold of them so I went with STI pinks. I haven't had any experience with H&R springs so I can't make any comparison there.
The result was excellent. The new springs actually raised the rear of the car (only due to the old springs sagging so badly) and dropped the front by what looks to be pretty close to the advertised 15mm. The car now sits nice and flat, I could probably handle it being a little bit lower but don't know if I'd want to go too much more than it is now (I did load it up with 5 people + bikes + gear for a long weekend and it was sitting pretty low). I find the 15mm drop a good comprimise, it feels great to drive, looks good and I haven't scraped it on anything as yet.
The ride height now sits at 360mm front and 340mm rear measured vertically to the guard. The ride is firmer (but in no way harsh - I commute in it every day) and the car handles much better (probably helped by a new rear swaybar and anti-lift kit done at the same time). The weight now transfer much more consistently when changing direction, it doesn't pitch so much during braking and over bumps and the body roll is signifcantly reduced.

