It seems the NVIDIA driver is NOT reading my (hardware-)EDID correctly, kinda bogus I know...
So someone helped me pointing out there a simple small program, freeware:
"Phoenix EDID Designer" http://www.tucows.com/preview/329441
This program lets you create a EDID-file. The NVIDIA-drive is actually able to read that correctly!
1. Open the program with wine or in windows
2. Import/ read your EDID file
3. Export it to raw-format, which will create a 128k file
4. add these lines in your xorg.conf:
Option "UseDisplayDevice" "DFP-0"
Option "CustomEDID" "DFP-0:/path/to/your/custom/edid-file/nameofedidfile.raw"
5. Remove all the crap you probably already have added in your xorg.conf (with all respect to all the helpfull people)
6. logout, kill X, startx
7. change resolution tot the correct size
8. Request NVIDIA to fix their driver :P