The way people respond to these types of comparisons really shows what kind of photography they do. Anyone who has ever done much wildlife photography knows that the longest telephotos become feeble when the subject is either small or distant, and people with this kind of experience know what its like to have a large frame of nothing.
Of course, if you start adding conditions then the thought experiment will be expanded and the choice maybe different. If you had just one shot left, on the basis that all the other shots on the card contained essential information and could not be deleted, and, if the angle of view of the lens was such that the FoV with both cameras (from your stuck position) was not cropped by the window frame and the interior of the room, then the larger format camera would provide more general information and any loss of specific information might not be relevant.
However, as you can see in some of the charts I've posted, the difference between the 20D and the 5D can mean that the name 'Norman Koren' is either legible or illegible, or in the case of the thought experiment, the type and model of a tank partially obscured by foliage, certain or uncertain.
However, the reason I did these experiments was not just to confirm that the higher pixel density 20D could resolve more detail with the same lens from the same distance, but to confirm that it could so so even at f22.
Having recently come across the following chart at Roger Clark's site, which relates diffraction spot size to f stop number, it would seem to me that resolution at f22 with a small pixel camera such as the 20D should be very poor.
Unfortunately, since I don't have any in-depth knowledge about much at all, I'm at a loss to explain how a whopping big Airy Disk 28.5 microns in diameter can permit a camera with a pixel pitch of around 6.4 microns to do so well at f22.