A few things which you can disable/change to make things go quicker and make it easier on a computer, though you already have everything turned down, I'm just throwing these out for everyone:
First of all, disable shiny water, never use it, ever, there are so many glitches, both minor and serious, which are caused by it, including random teleporting, game crashing, and file corruption.
Sky boxes are also something which can be turned off if you're having problems, it will help a lot if you've a weaker computer.
With shadows and grass, it is sometimes best to leave them turned off or at their minimum setting, especially when there are a lot of people/monsters nearby, and environment shadows also uses a lot.
Press alt+enter to exit fullscreen mode (Not sure if you can do this without altering a file), and play at a lower resolution, this works wonders on weaker computers, and I do it with some of the more graphically intense games that my older computer simply cannot handle, like Unreal Tournament.
And finally, something which helps quite a bit, open up nwnplayer.ini in notepad, and at the end of the list in Game Options, add in a new line that reads Max Memory Usage=##, put in a number for the amount of megs you want it to have. I've had it at 64 for a while, as that's what the place I found this tweak at said was the max you could set it to, but now I've found folks setting it to 500+, so I'm at 512 right now, though I can't really test out how good it will be until next week...