I can't tell if this actually helped, and I don't want to keep restarting DAI to test it, but it seems like it might have. The game did still stutter terribly as it was loading the menu, but the menu itself was smooth, and it stuttered terribly again when it loaded the save, but it's smooth in game. So success, maybe?
Whether this worked or not, I do agree that the stuttering problem seems to be CPU related, at least for me. When the game is running smoothly, I hover around 70% cpu usage for DAI (I'm using a little old i5 750), but whenever I start the game, it jumps to 95+% and stays there, stuttering all the while. Frequently it freezes completely and I have to restart. Disabling one core keeps it at 75% (of course), and it still says there and stutters terribly, but it seems like it freezes less often. So that's something.
It's incredible that they didn't catch this in QA. But anyway, thanks for the suggestion!