I wouldn't go any larger than a 2" on a 4AGE, maybe 2.25" if you are lookin at a GZE.
to answer your question about supercharging a GE, it can be done but when you add up all the costs of doing it, and the headaches, it comes out much cheaper to just buy a GZE and put that in. then selling the GE....
GZE's are also a much better base platform if you plan to turbocharge it down the track.