Actually, I wasn't gonna say anything about your PC
Anyway, look above your health bar. There are 4 buttons.
Click the fist one whenever you go into one of the 4 cities I mentioned, or Archosaur. It temporarily turns graphics down. When you leave, click it again and make sure the 3rd button isn't green.(If it is, click it too.) the 3rd button removes the avatar of anyone not RIGHT next to you.
You will always always always have to use those two buttons in archosaur, that's the capitol of the whole game where everyone sets up shop. Even people with high end comps have to use those settings during prime gameplay hours. And most of the quests after level 20 are dispatched from that area.
Yeah, it's a pain, but overall those are the only places that generally happens. If you get that frame rate while in an unpopulated area, then it IS in fact your PC. (Unless you're on an overheated laptop...but then again, that's its own issue...)
-Twilight Storm
Yeah Storm, I know about that button. It automatically turns ALL details to the lowest setting, except for the textures. Allow me to say, that its pretty pathetic that the developers did that, instead of just optimizing the game just a little.
To understand the extent of it, (I see you've played NWN 2, good.) Imagine NWN 2 with Max details, and a city with 3 times more people than what I saw in Raging Tides (Tideborne's city), that can run on my PC with more 35 FPS, when in PW, it goes up to 14 FPS, LOL.
And if I have to turn down the settings of the already poor graphics to the lowest, to enter a city, (being ultra-ultra low), then forget it. Its really humiliating for me to do that.
Also, no its not my PC. I dont even have a laptop for gods sake. Its a C2D @ 3.2 GHZ, GTX 260 gfx card, and 4 GB of DDR2 memory, desktop PC.
And when I turned the graphics to the lowest (that pretty button you said, thats the first thing I tried, because tooltips said that it was to improve performance and decrease quality), in the city, it went up to 35 FPS, LMAO 
When I left the city, I hit it again, to increase quality, and went up to 39 FPS, with max details.
Like I said, if I have to do that, to get a playable frame rate, then forget it. This game, earns the special award of "Most unoptimized game of all time", de-throning MS Flight Simulator X.
I dunno what else to say, some gamers dont mind terribad gfx, while others have certain min requirements. I belong in that category, I cant stand terribad gfx, unless the game is Really good, and runs perfetly smooth of course.
PW seemed to me like a REALLY good game 
but graphics = 
and game optimization = 
And thats all I have to say about it. I'm sorry Storm 
"Can I haz cookies nao?"
