This all still seems pretty unusual to me for an otherwise capable GPU. What kind of setting are you using for Water and Mirrors? Are the other graphics related settings in Game Options on medium or higher for the most part?
If it's not any of that, I wonder if maybe @SimplyJen here or Nitromon back on MTS might have some suggestions for GPU settings outside of the game, in the Control Panel or Inspector, that might help. I'm on an AMD card and have a very different toolset so can only guess as to how to proceed on Nvidia.