I had a 3x, then went to a PA900, after using it for a few months, I went back to 3x because I missed some of the live controls, and it sounded somewhat different. So I pretty much can agree with your thought process.
The PA4x is MUCH better even than the 3x. You will love it. New sound generation, great new guitars, pianos, saxes, nice tilt screen, ability to use FC5 foot controller, direct play from USB.... and more. It's a big step forward.