oh, and as far as your catch-zone/MIDI track question is concerned, I think the reason using MIDI tracks sounds less transparent is because it's not using catch zones at all. it's just looking at the MIDI note that's playing and is being like "OMG I MUST CORRECT THAT PITCH!"
I think the only reason it doesn't sound transparent is because of how a note behaves when it enters the catch zone. even with the most conservative Preserve Expression and Correction Speed settings, you can hear exactly when a note enters the catch zone, because the pitch jumps noticeably. so unless the note already starts out somewhere within the catch zone to begin with, you're always going to have those weird artifacts. not exactly useful for those lines where you might be quickly sliding up into a pitch, or if you're close, but just outside the zone at the beginning of a particular word.