If your graphics card and CPU are quite old, maybe 70-80 fps cap is good enough, although more is better. After trying most graphic settings in this game, I can tell texture quality under 50% won't make it smoother, but the shader is important (go for low or medium), and, especially, turn off HDR. You can lower the details of trees and grass, and also you could forget about shadows if that helps your framerate. Fast water reflections makes the water look a little worse, but it's better for fps, and never use anisotropic filtering.
Many games, like RTS or RPG, can be run perfectly with VSync on, but some others, like FPS or this game, require a higher framerate in order to play better, in my opinion.