Why does The Witcher 2 run so Choppy?

Witcher 2 is not optimized as it should be by default,then the new crossfire/SLI technology is known to make performance issues simply by bugging drivers/game engine especially in older games.

So having up to date drivers and game is a must.

Other than you are left only with tweaking the user.ini file in witcher and making it read-only.

Here are the values and more information.

Maybe you have the DRM version of the game. DRM makes the game lag. If you got the game legally (through retail buying or online), you can go to www.gog.com and there you can download for free a DRM Free version of the game. Check it out and let me know.