Yeah, my ancient 2008 MBP still hammers along like a champ. My new mac pro is same as yours just less ram, 16gb. I'm also only working with clips about 4-5 seconds long, so length of clip doesnt seem to be changing anything for me. Autosave is off. The machine clearly has plenty of resources for the job.
I just got an update to AE a day or two ago that seemed to help a little. I also started working with .jpg files instead of .cr2 and that seems to help marginally too. Still, even when I get a sequence to stabilize, changing a parameter such as going from perspective to subspace warp can cause the autosave loop to occur. It's like trying to edit with a grenade, you never know when its going to go off but you know the pin is laying on the ground. So now i just manually save after every action that doesn't cause a crash.
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