(RESOLVED) Penumbra Performance Problems?

[MercenaryForHire]

RESOLVED
Installing the older NVIDIA 80-series drivers fixed the performance issues. Other users of the 90-series should try downgrading to see if this resolves their problems.

Penumbra's performance seems to be schizophrenic at times.

http://frictionalgames.com/forum/attachment.php?aid=214
This is at 640x480, all graphical options off, Very Low shaders. Basically Quake 1, and that's being generous. I'm getting a whopping 4fps in this screenshot.

Now, you might think that my system is just hosed. Well, check this one out.

http://frictionalgames.com/forum/attachment.php?aid=216
1280x1024, everything on except Motion Blur, AA, and AF. And this is getting 30fps. With the flashlight on, which is an extra demand on the graphics card.

Now, take a look at this.

[attachment=220]
Same high detail, but lowered to 800x600. (I was experimenting.)

If I look at that map directly, I get 60fps.
If I turn to the left about 45 degrees, I get about 40fps.
However, if I turn 90 degrees to the left, and look into a dead end, I get less than 10fps. There is nothing to render. Why is performance so horrid?

I'm reinstalling the tech demo to see if that runs horribly too.