If the 4" lift isn't causing any problems, why go higher? :dunno: a taller truck leads to a higher COG, and a higher COG than necessary is generally a bad idea, especially on the street and especially since your track width is still about stock..
If you're itchin' for a project, what about WJ control arms, a big ZJ swaybar, and a proper track bar? Just make sure that the trackbar is good for 4-6" so you won't have to replace it twice should you change your mind later. :thumbsup:
How is your rear lifted now?
Oh, and check with your local muffler place. chances are if you walk in with an axle and some perches, they'll burn it on for pretty cheap.