My thoughts.
The Pa4x is Korg’s flagship model. The Pa1000 has many of the Pa4x features.

If dollars are a problem the Pa1000 is the choice. If not, buy the Pa4x it leaves little room for regrets.
The only two (important to me) differences I see is internal speakers and the weight of the keyboard.

I guess the better question should be is what do I want in a keyboard. I bought every model of Technics from the Kn2000 to the Kn7000 by fate in the product. I have owned the Pa800, Pa900, and now the Pa4x. All my decisions were made by reading what was posted here on Synthzone, and YouTube – and fate in the Korg product. Is it the best keyboard out there? No, because the question is wrong. It should be – Is this the best keyboard for me?

Opps, on my soapbox again.
John C.