Re: Feature Request - option to disable panning for mode switching.
Sorry to say but this is not a problem of the nvidia drivers. The highest resolution in a Mode (display section) or Metamode (this is an nvidia feature) is chosen as the primary resolution in case of twinview for both devices. In all cases when lower modes are added they are virtual resolutions.
Since some time there's an extension called RandR which allows resolution switching but it doesn't work in conjunction with Twinview.