Just in case: For Blu-ray movies you set the PS3 to 1080i
Then your Bravia will take the 1080i signal that and fit it into your panel's resolution. (You leave 720 selected also, for 720 games)
Results should be similar to your hi res DL files.
Since you asked, a true 1080p in/out display could display about twice as much data so that would mean a 56" at least, in equivalency to what you have now.
Carry on