A simple way to get a feel for the greatly increased distance between keybed and buttons would be to simply put the PA1000 on the top tier of a stand and put whatever controller you want underneath it, MIDI the two together, then try to play the bottom keyboard while having to reach for the top keyboard's buttons, sliders and knobs.

For the sake of experimentation, bring the top keyboard's buttons in close enough that, if the Korg's keybed wasn't there, the controls are where you'd place them while still being able to read the bottom keyboard's display and get to its controllers.

I remember playing big multi-keyboard rigs back in the day when there were no other options, and the distance my hands had to move to get quickly and accurately from one to the others was definitely a factor. It's no coincidence that the keyboard DESIGNED to go quickly from one manual to another is the organ, and there's NOTHING between the two manuals, going from one to the other on say a B3 is virtually instant.

I would still counsel playing the two keyboards MIDI'd together and see if it works for you before you take a hacksaw to your PA1000. That will kill its resale value, and the way Korg is going, the PA1000 may be the last MOTL arranger Korg make. That's going to keep its resale value high if no better successor exists...