Welcome to the forums, and glad you're enjoying the game!
Most likely if your performance is bad, you'll want to disable the machinery in the walls and the ground fog. If that's still not enough, then disable additive blending and restart the game, and see if that does it. If not, also disable vsync.
Enabling "destroy materials" and "destroy sprites" may actually hurt your performance if you are more CPU-bound, so probably best to leave those off unless you really have to. The additive blending effect won't really kick in until you actually restart the game if your graphics card is one of the ones that has trouble with that sort of thing. My mac doesn't have that issue, but some folks on linux were, so it really just depends when it comes to non-windows machines.
If those don't work, then added details would be appreciated. You can turn on the FPS display and let us know what some values are there as you are playing, and so forth. Ideally the game runs at 60fps or more, but it is reasonably smooth even at 30fps.
