Yes it's slow with multiplayer and singleplayer. Multiplayer nearly froze on mine but I got to slip a chat before I left hehe. 64 Meters barely does anything on mine.
The version I uploaded just now will nerf the shaders if you hit F8 (it's pretty ugly but this is just a test). It turns off per pixel lighting (no really proper lighting at all for that matter) and turns off bump mapping, normal correction, etc... anything I could get away with shutting down.
If this significantly increases your framerate then it gives me something to work with in the future.
Another thing to try, in the single player game go to the bottom of a deep ocean. If the frame rate goes up dramatically then your GPU may have the same problems that one of my cheap cards does. I narrowed that down to the number of textures... shrinking them didn't help at all. I will have to go with a texture atlas to improve those cases and that is something I'm pushing off until after alpha.
