My partner bought the 5600AB model at the same time I bought my Ultracast 5600. I still have the Ultracast and am loving it. He sold the 5600AB and got a ultracast, he's a lot happier now. Once you learn what your thumb is for, the AB feature isnt worth the other tradeoffs, and the reel will never cast as far as as another similarly sized reel.
for what it's worth, we use Gamakatsu line, the 14# has the same diameter as normal 12#. You get more line on your spool, and I think it casts better.