The framerate in cutscenes plunges down to 20 fps. Performance outside of cutscenes is flawless, anywhere between 70 and 100 fps. Somewhat amusingly, there is no noticeable difference in performance when I switch between the default medium and high graphics settings.. My computer exceeds the recommended requirements, so something strange is definitely going on!

Specs:
i5 2500k
AMD HD4870 1GB
4GB RAM
Win7 x64

Things tried so far:

-Lowering graphics settings - No noticeable improvement in performance

-Lowering resolution - Very small improvements, I gained 3 fps going from 1920x1200 to 1680x1050. The framerate spikes in cutscenes are still there, so it didn't actually help. (As a sidenote, I'm aware that custscenes look "chunky" in 16:10 mode. 1900x1080 did not fix the fps issue.)

-Forcing Vsync through Catalyst and ATI Tray Tools - I saw this suggested in another thread. Didn't change anything.

Any help would be appreciated!

Update:
New problem, magic effects cause severe slowdowns in-game. The fight with Savolla takes the fps down to 14.
On the plus side, I didn't realize that I had depth of view turned off. Enabling it improves the cutscenes, although the framerate still dips noticeably.

Update 2:
-Tried reinstalling directx 9.0c - no effect
-Switch to windowed mode - no effect
-Set lighting to low - Better, no dips under 30 fps.

Reducing the lighting is a fix... sort of. My graphics card was considered high-end when it was released, a year after The Witcher. Something is stopping the game from performing as well as it should.

The "choppy cutscenes" problem is covered in the sticky thread. Try toggling the "depth of field" setting in your graphics options; this fixed it for me and many others.

Don't know about the magic effects, but my guess is that the lighting setting was the culprit. Anyone else know?

Yeah, I mentioned that enabling depth of view helped the cutscenes somewhat. Sorry, my post was a bit all over the place, as I was updating it as I was trying various fixes.

I wouldn't say the lighting settings are the culprit, if only because they have such a severe impact on a system that exceeds the game's recommendations. Maybe I'm expecting a lot out of a creaky game engine, but it makes me wonder if there are some driver issues or something else going on. Updating my gpu's drivers hasn't helped though.

I think in some cases the lighting settings really do have an enormous effect on performance even when the hardware should be able to handle them. This is probably a driver issue, as you say, but I think a lot of players were never able to fix it except by disabling lighting options (i.e. new drivers never fixed the problem).

Again, though, I didn't have this problem myself so I'm not sure. Anyone else have more info?