Your Vocalist will blow away any arranger built-in harmonizer. Maybe Korg comes close, but you've already nixed the TOTL arrangers. You've already got the Vocalist, stick with it!

Pay careful attention to the drums in the PA600 vs. the Yamaha's. Depending on whether you like a good live sound or want a more polished, CD-like sound, this may make a difference to your choice.

And, as budget seems to be an issue, take a good listen to a Roland BK-5 as well. Very punchy drums, loads of styles (probably more than the Korg) and a decent action... and nearly half the price of a PSR S950.