I've actually been pretty happy with my PC's performance. I have yet to experience any stutter whatsoever, and the only place I've seen the streaming result in any texture pop-in at all was the inn in Flotsam (happened very rarely, once or twice in the 15 or so times I went through the inn). I didn't look at average frame rates, but I honestly don't care about the exact numbers as long as it is high enough that nothing seems 'off'.
I run TWitcher 2 at 1920x1200, with everything on highest settings/enabled except the following:
Texture Memory Size (set on Large)
Shadow Quality (Medium, still looks nice, can't see much difference between it and High)
# of Shadowed lights (High)
Depth of Field Gameplay (Disabled. Turned it on for a bit, and not bad performance, but I didn't like how it looked)
Motion Blur (Disabled. Not sure how it might affect performance, but I don't like how it looks.)
Cinematic Depth of Field (Disabled.)
Dangling Objects Limit (Disabled. I think this is actually a higher setting than enabled.)
Vertical Sync (Disabled, cause I don't get tearing.)
Processor: Intel® Core™2 Duo CPU E8400 @ 3GHz
Graphic Card: 2-card SLI GTX 260 (216) (Both are XFX Black Editions, which actually perform better than 280s in a number of games, so don't necessarily look at this as representative of what you'd get with another 2x260 SLI rig)
RAM: 4 GB
Operating System: Microsoft® Windows Vista™ Home Premium (64 bit)
Mobo: Can't remember off the top of my head, can't be bothered to look.
Since my build is no longer an especially expensive or new one, I've been a bit mystified by all the people with performance problems.
TWitcher 2 is the first game that I haven't been able to play on the very highest settings at 1900x1200 in the 3 years since I built this PC. So I probably have a few more years before games that I can't play on any settings come out, and it's upgrade time.
--Too Dumb to Quit--