I installed RC's 6.5" X-Series suspension nearly 2 yrs ago and love it! The only issues I've had or have with the kit is that it didn't come with shims (which were badly needed due to pig to driveshaft mis-alignment) and the front shock bushings crapped out on me (I was in a pinch and rigged it with some rubber I had laying around my garage so I didn't have to hear my shocks flopping in and out of the wheel well). Perhaps polyurethane would be the ticket here?
Initially, the ride was fairly stiff..but liveable. I wasn't terrible impressed with the flexibilty of the lift at first (particularily the rear springs) so I ran w the discos pulled for a month or so forcing the rear springs to work harder at stabilizing. It worked..softening them up and making them flex much better.
I didn't do any floor to bumper measurements after the lift but did notice the ass-end sat slightly higher than the front for about a month. The rear has settled (leveled) and has not sagged any further..(noticeably) at all..in nearly two years. Ther front now flexes good enough that it ran the sway bar bolt through my drivers-side wheel well while messing around offroad last year.
Last thing, I noticed that ride quality reamains decent as long as I keep things lubed, tight, and aligned. My 2 cents. :greensmok