That would mean going from 3200 to 6400, if you take it literally. AKA a single stop noise performance.
But there is always the possibility of Canon making simply a certain range of settings available, and the true change is in image quality.
Say the sensor creates 1/3rd of the noise. this could translate to one stop higher settable sensitivity with improved noise and shadow rendition, or an additional H-setting with worse characteristics.
But being backlit wouldn't help a large sensor as much as it does for a small one, I wouldn't expect wonders without taking hints from the 1DIV's design.