Hi Kimberley Crusader
Go Jeep has been helping me sort out some vibes I have been having with my 4.5 lift with SYE (Flange style).
I have single cardan joints and have spent much time (read: 6 weeks) sorting it all out. Firstly my pinon angles where 'out' (this much be sorted if going the single cardinal option, very important), secondly found that my 'new' drive shaft was out of balance and that the flange was warped. Getting the new flange fitted and drive shaft re-balanced tomorrow, finally.
In summary, make sure you get a good drive shaft built, a double cardinal is a luxury, however also know that a single cardinal will mean a transfer case drop (probably).
If I was doing it again, I would go the double cardinal (although have never had one), although have been told that it will not always solve vibration problems, however you will not have to drop your transfer case.
Good luck, hope I helped