See this thread here for a before and after picture of my car about a month after the install:
http://legacygt.com/forums/showthread.php/need-suspension-01-legacy-gtl-sedan-171330.html?t=171330&highlight=stoggy
Now look at the pic below. About 12000km after install.
http://i1179.photobucket.com/albums/x387/stoggy95/subaru_handr_zps71ac011a.jpg
I think the pics speak for themselves. The rear, as you said, is not the same ride height as the front. You noticed when you installed yours that there is a rake to the vehicle. Mine had a rake too, obviously. Keeping in mind the relationship to the front ride height the rear has dropped 1-5/8" and the front has dropped 1-11/16" from the measurements I had from stock. To put it simply, the rake is still there, it's just lower all around. It DOES NOT sit level like you are looking for but it is definitely lower than your car is fresh after the install. With your King Springs when you have a load in the truck or people in the back etc you will have a saggy ass end which is (to me) unappealing. I am happy with the rake. I've had over 550lbs of shit in the car and it sits nice and level and doesn't bounce or nothing.
About the 'settling' period for springs, it really depends on the brand of struts, the driving style and how many km are on them. I have never seen springs settle in 500km, it just has never happened for me. I have always seen lower results with any brand (I'm talking, Eibach, H&R, TIEN, HKS, King Springs, OEM, etc). I've literally installed several dozen coil springs in my life--both factory and aftermarket--and they always take way longer than 500km to settle in.
That said, this is the internet and most of it is make believe. I'm speaking not from the internet but from my personal experiences on various vehicles from cars to semi trucks with leaf springs and air bags. Even air bags settle.
Just my .02 on that matter.