Yes, actually I have 112 separate vocals in this song, so a lot of regions using flextime. I suppose you're right, Logic is hitting it's ceiling.
Another thing I noticed is that the regions will often go out of sync with eachother. In my opinion, the system should not play rather than present the audio in any other way than it's been produced. I spent hours corrected the vocals, which are quite rhythmic. Sometimes when they play they sound perfect. Other times they begin to drift. It's so frustrating!
I'm not sure of which response by sammydave you are referring to. If it's the simplification of the song, yes, that's my next step, unfortunately.
I'm working on a 2009 MBP with 8 gigs of ram. Do you think if I purchase a Mac Pro with 16 gigs of ram the problem will go away?