read that. it's been confirmed by multiple people. you load up the rear with a WRX/STI suspension and the control arm will hit the body or frame potentially causing failure, damage and discomfort. just because something can bolt right up, doesn't mean it should be done.
jmackoul from subaruforester.org said this.
What i'm talking about is that with the sti/wrx suspension, the upper control arm is very very close to the chasis. when and if you have over 300lbs load in back seats + a passenger, in other words, a full car, the upper control arm will actually rest on the chasis. This is because the impreza has a bent upper control arm and the forester has a straight upper control arm. This is why some people that have swapped for the sti suspension opted for a 1'' top hat lift kit front and rear. Slamming the forester isn't a mechanically sound mod unless you swap out the straight upper control arm for a bent impreza upper control arm.
I don't plan on swapping to the sti/wrx setup. Based on portbarton's (Philippines) review of them on stock springs, the dampening rate is higher and provides a slightly firmer ride, although he does emphasize that they are not a sport strut. SH owners interested in the KYB's hope to mate them with swifts as this should provide a few things:
1) a better dampening strut that is better than stock
2) a strut that can easily handle the 1'' drop from the sift springs
3) a comfortable strut
IMO, struts and springs are not the crux of ones suspension. sway bars, end links, springs, and subframe bushings are really what can make a comfortable daily driver turn like a track car.