Very low FPS

[micromancer]

Some additional things:
Changing resolution makes the game crash upon loading a mission (main menu works).
The game uses 85 % of all my four CPUs at all times, but if I block 3 of them so the game uses only one I still get 8 FPS, no change.
I really ALWAYS get 8 FPS. Settings don't matter, In Main Menu, in Battle, I can Pause, I can increase speed, it always stays at 8 FPS.

I really have the feeling this is a very specific issue I have here, because I can't explain this behaviour otherwise. What really puzzles me is why the CPU usage is so high and why I can do what I want, performance always stays the same.