Rear Leaf Spring Variations???

I have read many posts on here telling XJ owners to install a set of "Heavy-Duty" replacement springs to get a little lift over stock. We sell 6 different rear leaf springs for 1984-2001 Cherokees all from Crown Automotive (the same place Quadratec gets them). In Crown's dealer catalog, they have them listed as follows.
520000051AB Standard - Quadratec lists as "Standard Duty"
4886185AB Heavy Duty (LS, ZGV, ZVV)
4886186AB Heavy Duty (LT, ZGW, ZVW) - Quadratec lists as "Heavy Duty"
4886187AB Heavy Duty (LK) - Quadratec list as "Medium Duty"
52000706AB Heavy Duty (LN, ZUU, ZFU)
52000707AB Heavy Duty (LM, ZGU, ZVU)
Does anyone know which are the "Heaviest Duty"? Second heaviest and so on?
I would like to be able to supply my customers with the most accurate information. Believe it or not, Crown had no answers.

You can view our selection at http://www.jeep4x4center.com/jeep-suspension-parts/84-01-cherokee-xj.htm

I've seen a thread where someone had researched this, maybe Jeep Forum. Sorry I can't be more help, but I know the information is out there, I've seen it.

This may be the thread you're thinking of. See the posts by "Whatevah". IT's a bit confusing because there was a misprint in Quadratechs catalog at the time.

http://www.naxja.org/forum/showthread.php?t=959538