OME sells a 3" kit for the XJ (the expedition duty leafs and taller series coils). I wouldn't spend the coin on OME to get to 3". Their kit is designed as a perfectly optimized suspension for the factory design, and raising it doesn't do any good for the extra coin over other options (I've been there and done this). Either stick with the 30's and OME (a very capable setup) or move on to different kits. But, if you are hung up on OME, look into the taller kit.
As for OME ZJ, the ZJ lift is lower than XJ for OME. I don't think you'd get any additional lift on an XJ.
Nay