I have 8000 miles on a 3" lift on my 2010 JKU Rubicon. The front shaft is still ok, but I expect the joint boot at the tc to tear in the next 8000 miles. When disconnected, the front shaft will hit the skid plate (notch it for clearance) and the auto trans (just slightly) if you have one. So far everything if fine. I picked up a spare set of new driveshafts for $200 to replace them when they fail. From what I've seen, I wouldn't want to go any higher without double cardon shafts.
1997 ZJ..... still building and getting there
1997 TJ, Stretched, 1 tons, 42" Pitbulls, 350,