Does the fps vary from location? Start by turning off vsync. You might try windowed mode as well. Some games run better in this mode. Did you try lowering the graphics settings to a minimum temporarily? Turn your attention especially to water refraction option. Turning it off may give a massive fps boost. What's the version of your graphics driver?

How long since you did a cold reboot of your computer?
That might fix it.

Sounds like you had the same issue I did on my system, and my rig isn't as updated as yours (8 core, 16GB, same video card). Is it where the audio plays fine, but when clicking to move the characters it seems like it jumps? Rebooting the PC every few days fixed it for it me. I remember reading somewhere that the game was using something based on the system uptime (I don't remember the exact details). The other thing I did was install the Client Extensions, which let me avoid rebooting it as often.

Another thing, you wouldn't have happened to have a previous installation of NWN2 on the computer that might have older mod files in it that it's trying to read?

None of those options mattered. It is the same issue people are getting where they said puttling the DLL file in the directory solved it for them, however for me, it didn't solve anything.

All drivers up to date with current release, OS patched, etc.

It is the game itself. Something is causing massive FPS issues in the actual game. The solution was supposed to be that DLL drop-in, however, it isn't working. Something minor must be missing. I'm having the same issue as here: https://www.gog.com/forum/neverwinter_nights_series/disc_version_gog_and_the_stuttering_movement_bug

The DLL drop in was supposed to fix it.

There is a 3rd party program which fixes it, and my FPS jumps as high as I want it to be (500+ if I'd like), but I don't want to use a 3rd party program which also acts as a game server. I just want to resolve the FPS issue.

Any ideas anybody?

Known problem, just reboot.

It might not be the stutter bug.

IIRC, the stuttering movement bug, only affects character movement. Rotating the screen is still smooth.

Another thing is that system reboot also fixes the stutter movement bug.

The longer your PC is on, the worse the stutter bug gets. I seldom reboot unless forced to, so it was so pronounced for me, the characters seemed to be stuck, then teleport 10 steps away.

If a reboot doesn't fix it, it isn't the stutter movement bug, and the DLL drop in won't fix it either, and neither will the NWN client. They all solve the same issue.

I prefer the DLL drop in as the cleanest solution, and it has completely fixed the issue in two of my games (NWN2 and Jade Empire).

If it isn't the stutter bug, it might be your NVidia drivers. They often release new drivers that kill old OpenGL performance and it goes without notice as not many games rely on it.

You could try older and new NVidia drivers.