A tip for Vista users I haven't read here before and that solved all of my stuttering problems:
Install the game to your home directoy/drive (so, usually C:\*) and not to any secondary partition or alternate physical drive. Vista combined with some games/copy protection seems to hate that...
Installed on drive D in my case: stuttering video sequences, stuttering speech and audio, a MINUTE of delay before opening the options menu or initiating some dialogues.
Installed on "C:\Program Files (x86)\Divinity II - Ego Draconis" and it runs smoothly in 1680x1050, max settings...
