I have made similar connections before, and found OneWorld reps at the gate of the arriving aircraft with "fast-track" passes which somehow got me waved through the diplomatic channel at immigration and then escorted back through the TSA check-point - no idea if that is unusual but it has happened twice now for me in Miami. This wasn't a case of IRROPS or delays either - just a regular booked 'tight' connection (which actually left me 30 mins spare in the lounge!)

MIA immigration is quick now (generally) even without GE. With GE and the TSA-Pre which comes with GE you should be OK, especially if you don't have checked bags (which is the slowest part of the process at MIA).