I've been playing a bit with the new build and while it seems it is an improvement I still have some issues.
I'm going to make a little recap of my experience here:
Jerky mouse movement – The mouse doesn't response correctly ignoring any movement for several seconds, the only way to fix this is changing the priority of the incubation process in the task manager to "Above normal" or "normal".
No music in game (menus and in mission) and no sound in cutscenes – If I use alttab I can listen the music and the cutscene audio while the game is in the background. As soon I come back to the game the sound stops. When I'm playing a mission the music suddenly starts playings but for less than a second.
Jerky mouse movement – It's more smooth than the mouse in DX mode, but not as good as if you change the priority of the process in task manager.
Music (menus) – It plays correctly for a while and then it stops and resume repeatedly.
Sound in cutscenes – It doesn't play smoothly, also it seems that the
cutscenes itself plays a bit slow so the sound gets out of synch. (The sound ends earlier than the action in the cutscene)
In the end it seems that 3Dfx mode works a bit better than DirectX and let me play the game.
Just in case, some months ago I had a conversation with gog support about incubation, maybe it can be useful.
P.D: Sorry for my English, I know it's not the best :S