It was definitely the amount of pre-comps that was killing it. I just went back and checked, and there were over 300 layers. I always thought that only the layers being displayed demanded the horsepower- and so the amount of other layers wouldn’t matter- but that’s apparently not the case. I’ve completed several other smaller jobs and they were all pretty zippy, and definitely faster than my 2008 MacPro. 🙂
Pre-rendering definitely helps. And the multiprocessing settings that Walter recommend made a big difference, too.
I actually received an email directly from an Adobe rep after my similar post on the We Want A New Mac Pro FB page. Lou Borella, the site’s owner, was able to hook that up for me. He mentioned as well that they will be focussing on performance in the upcoming year, and said, specifically, they were looking to separate the render thread from the UI thread, which is great. I look forward to that update alone.
Thanks again, everyone, for your responses.