I have the same issue, and would love it if GOG would be able to find a real fix. Other fixes don't really seem to work: CPU killers make the sound choppy, and cranking up the graphics settings just makes the framerates inconsistent - depending on where you look, the framerate varies wildly, so you slow down while looking at fire, and speed up looking elsewhere.
For what it's worth, I'm using an ATI card in a Lenovo T60 laptop. Forcing Vsync (ATI's "Wait for vertical refresh: On") doesn't help, and I've tried many of the different video drivers. rOpenGL does seem to produce the nicest rendering, and once and only once it ran the game at the appropriate speed, though I have serious problems with vertical flickering when using that driver.
This game is pretty unplayable in its current state for me (and obviously for a number of other people.) It would be nice to hear something more from the GoG staff than just, "We've fixed this, don't worry" considering it is still clearly a problem for many users.
That said, this is the first GoG I've had any trouble with, so that's a pretty good record!