My Group 4s finally came, and I had MPJ install them last week. I've been playing around with the ride height and stiffness since then, got it aligned, and spent some time today around the mountains. I've had really high hopes for these things, as I want a certain level of comfort while increasing performance; you may recall my "barf" thread where I complain about the weird jarring on the stock STI, most likely attributed to the inverted struts. I also have issues with most of the other coilover options, such as maintenance, extremely high spring rates, no US support, etc. The verdict is: the Group 4s have made me very happy!
These coilovers have a 46mm piston, non-inverted monotube design, with 275/225 spring rates. The adjusters are on the top, so the rears come with a cool knob-extension that places the adjuster slightly above the rear seat. From the back of the car you see these weird little gold knobs peaking out - very clever! The quality of the welds and brackets is much better than Tein Flex's, HKS's, and H&R's, and the main seal looks impressive; you can tell they are quality units. They have a helper spring, and shock travel is apparently MORE than the stock STI. They are height adjustable by a gold ring with an allen set-screw. The dampening adjust has 14 clicks: I have mine set at 6 up from soft, front and rear. I had the rear set 1 click softer and the car seemed to plow; at "even" the car feels balanced like stock. My car also has an ALK, but the swaybars are stock.
At full soft the coilovers feel very similar to the stock STI - which I find weird as one is oversprung, and one is undersprung - but there is a similar kind of freeway bounce. Between 3 and 6 clicks the car feels very comfortable, and this is where the adjustment will live on my car. The jarring I experienced on my commute with the stock STI suspension is gone! The car still has that sporty feel but the ride is better tuned for a street car. Taking corners is completely different; there is much better control and the lean is dramatically reduced. At 7 clicks the car feels flat and stiff. I'm not sure why anyone would want it stiffer, but there are 14 clicks total, and each one has a measurable effect.
On the way to MPJ I hit some railroad tracks pretty hard and the stock suspension absorbed everything really well. On the way back I kind of chickened out, but it seems like the Group 4s would not be so kind to your butt if you still plan on jumping the car. I had to make the decision to turn my rally car into a "versatile street" car, and I held off on the swaybars because I really don't want to give up compliancy. But now that the Group 4s are so comfortable I feel like I can totally afford to have fatter bars, so that will come next. There is one thing I will suggest to Whiteline - that is nylon or rubber washers for all the spring-to-retainer contact areas. After a week these things started making the typical "popping" noise, of road gravel crunching between the spring seats. I loosened everything and wrapped the contact areas with electrical tape and the noise is gone.
I'd really like to thank Jim at Whiteline for putting up with all my emails, hassling him about various suspension setups. His website has a plethora of articles on tuning WRX suspension, as well as general kinds of testing and data. They have certainly made a believer out of me! My STI is much more fun to drive, and feels like more of a sports car in the twistys. Big thumbs up!