VoodooExtreme has a
short note from Arkane's Raphael Colantonio on the fixes they are working on for
Dark Messiah:
We're currently fixing a lot of the stuttering that happens with Dark Messiah on some hardware: We're modifying the way we're accessing some of the audio and precache files. A patch will soon be released for both the Retail and the Steam version. It fixes a lot of issues, including a few scripting bugs and some performance [issues]. We are really sorry for the problems some of you have had with the game, and be sure we're fixing them all.
…and they are also pointing out a
tweak guide at TweakGuides.
More information.