Thanks CDFN, got it installed now. Unfortunately, I'm going have to shelve it and hope for improvement in the next patch and/or driver update, or failing that, upgrade my computer. Going back to the old patch seemingly took care of the stutter, but chapter 2 is just too choppy to play. I've no idea why, but it seems to be much more system-intensive than anywhere in the prologue or chapter 1. Oh well.
Day 1 patch: poor FPS, no stutter = unplayable
1.1 patch: better FPS, terrible stutter = unplayable