When exporting Revit sheets to Autocad the Zoom Extents varies depending on which units you have selected in the export function.
I don't see why, when exporting sheets the Cad file cannot be set to mm (or Inches for those Imperial folk) and the extent is set to your titleblock.
Attached is 5 examples of the different units which has been set in the R > Export > Cad Formats > DWG
Currently what needs to happen now, is that there needs to be a script written for Autocad to set the extents.