Why is the Witcher 2 unplayable on recommended high settings?

I just got The Witcher 2 today and so far it seems quite enjoyable. The problem is that I haven't been able to play much of it so far due to lag that occurs even on low settings. The game recommends that I play on High, but this simply isn't possible; the game pauses every time I so much as turn Geralt's head. Any idea what's causing this problem and what settings I might need to adjust to get the game working at a normal, mostly lag-free speed?

My graphics card is the NVIDIA GeForce 9600 GT, and I have 4 GBs of RAM on my computer. My graphics driver is beta driver 275.27. All display specs can be found here(results from running dxdiag).

I made the following adjustments:

• Installed the latest beta driver from NVidia's website (version 275.2something)
• Adjusted the screen resolution from 1920x1080 to 1360x768.
• Uninstalled the 3D Vision driver
• Updated to Patch 1.1, which removes all DRM(apparently a cause of slowdown up to 30% on lower-end systems)

The game plays at around ~16 FPS on High settings with occasional bursts of lag when entering new rooms, and plays at a much more enjoyable 28 FPS on Medium.