The superlift replaces steering components to bring all the angles back to the stock specs. So theoretically you can add your current lift to the superlift and be no different in terms of CV angle that you are today. I would still want to fully research the front driveshaft interaction with the new crossmember and see how the u-joints would be impacted and make sure that the EGR module will function properly with the additional lift over 4". I can tell you that going from the RR lift to the SL was significant. After switching the 265's to 285's I am about 3.5" taller than the RR at the roofline. The rear diff is only about 0.6" higher than before, mainly due to the difference in tire radius.

Good topic and if stacking spacers can be done safely, then its something that I myself would consider in the future.