I was told by the guys at Clayton, that the front springs have a rate of 175 lbs, and the rear has a rate of 225 lbs. In my opinion, the rears are too stiff. Plus, the front end sat about 1" lower than the back (which is how they are from the factory). They said that the reason the rears are stiffer is to have extra load capacity for cargo and towing. I am not sure what the exact weight bias is, but i know its a lot more in the front, than the rear. I think the rate of the front is pretty good. Really smooth over bumps, but the rear doesn't move as much as it should, which annoys me. It doesn't feel balanced at all. When i go over a speed bump, the front is hardly noticed, and the back jumps around. Since i am setting my dub up for higher speed stuff as well, i will probably end up going down in spring rate on the rear once i get my Fox shocks tuned and installed. I am a lot more picky than your average guy because i design and test racing suspensions for a living. If i didn't know better, i would say the claytons are pretty good.
Now, when i added my winch and bumper on the front, i had to add 2" spacers to the front end, and now it sits perfectly level. Ride feels basically the same. The bumper is 112 lbs, and winch is around 65 lbs or something, if i remember correctly. So that would make sense on the 175 lb rating.. being pretty close to lowering it 1" with an extra 177 lbs i added.
I was told by another jeep guy that clayton has supplied 4" TJ springs which are softer for the rear of the WJ, and has a more balanced feeling. But that is just hear say.. not sure if true.
I don't have any expirence with the IRO coils, so i can't comment on them.
04 WJ, Limited, 4.7 HO, w/ lots of goodies
Incline Winch bumper from WWW.FRANTZDESIGNWORKS.COM