I also plan to buy a XP-60 primarily for the sequencer. After reading this I am concerned.

So today in a local musicstore I was lucky enough to test a XP-80 (and XP-60).
So I tried to crash the sequencer in the limited time and experience I have about xp.
I recorded 7-8 tracks. 3-4 tracks with 4 tones each. 4 tracks with 1 tone each (simultaneously). I did hear no slowdown, though a guy in the back of the store was playing really loud guitar with heavy distortion (hate when that happens...).

So either the slowdown was really small, or I erased by accident some tracks when recording (though I did hear at least 3 distinct sounds at playback). Or the sounds all had just 1 part.

I guess you have to play with it to see if you can live with it (in a more thorough way than I did perhaps).
I used to own a S-330 and W-30 which also showed very minor slowdown at limits but then again they only have 16 voices.

Thanks for all the advice. I love to hear more about this.

Lucien