My opinion
Sounds: I can't hear any difference. I used factory sounds, not legacy, in each model

Styles: almost identical. I hear more "live" the Pa3x, basses and drums, perhaps sounds less compressed.

It's been said in the forum many times that TOTL arrangers have more Rom so I would expect less compressed or more layered sounds. I did not notice that on the few I tried.
I chose similar sounds otherwise it would be unfair to judge the sound quality of each arranger. We all know the arranger's technical specifications and sound list by searching in the internet.

I'm very happy with my Pa3x. It sounds quite powerful to my ears, may be I can reach higher volume easily. It has also a more sophisticated Maxx audio EQ which can improve much more the final sound.

Not only did I pay for some extra sounds, I also paid for a very solid metal case (hadn't seen one so good for a long time), extra sliders, buttons, ribbon controller, DNC, EC5 pedal option and excellent keys (keybed) with aftertouch. I think most of the extra money you pay goes to the hardware. I was really very dissapointed with the Pa500 keys, it seemed they could be broken easily and didn't like the blue color either.

I would say that the Pa500 is a very good arranger. If you don't need all the extra hardware features and voice processor you get a good sounding keyboard.