For anybody running an AMD crossfire set-up (2 or more AMD gpu's) you might want to download the recently released AMD hotfix 11.5b, which "enables AMD crossfire scaling in the Witcher 2".
http://support.amd.com/us/kbarticles/Pages/AMDCatalyst115ahotfix.aspx
Before the hotfix, I was getting pretty poor performance running at 1920 x 1080, with ultra settings and I had to disable ubersampling, but after the hotfix I could play with ubersampling on. I just got my new monitor, Dell U2711 (2560 x 1440 resolution) and I've had to turn off ubersampling, but I'm still running on Ultra (w/o uber) and the game runs great. With ubersampling I was only getting in the 20-30 fps at 1440p, so I turned it off. Definitely get the hotfix if you're on crossfire.
I'm running on 2 x 2gb AMD 6950's (shaders unlocked to 6970's) @ 6970 core/mem speed in crossfire.
starcraft: "I and every PS3 fanboy alive are waiting for Versus more than FFXIII.
Me since the games were revealed, the fanboys since E3." 
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