Thanks for your help!
I already changed the xorg.conf and I had to fiddle a little bit more to get the nvidia driver to behave. Now it covers all of the correct modes. I am attaching the nvidia-bug-report.log
I have two little problems:
1. Now the driver only supports some of the valid screen refresh rates. For example I know that this card can support 1400x1050x75 but now it only goes up to 70. Why is that?
2. For some reason the glx is not working so I get the notorious "Xlib: extension "GLX" missing on display ":0.0"." from glxinfo.