I have been looking into these radios as well for me heres the biggest diffs for the extra money.
Dual microprccessor 12Z
Quad bearing gimbals
And the biggest thing for me is servo speed in flight modes, the 12Z is the lowest priced Futaba transmitter that gets you this feature, consider a JR9303 does this in a sub $500 tx.
ITs actually looking like I may just get the world X11 and my trusty FASST module to get nearer to a 12X. The FASST module will actually do 12 chnls IF there digital. So it's getting close. Besides I could sell off the DSMJ module and RX for a decent buck.
http://www.rc711.com/shop/jr-11x-zer...l?cPath=167_24