For example: How would a stitched 1ds image (equivalent to 22+ mp) compare to that of a mf image (excluding the aforementioned) assuming both images have same subject field of view & depth of field?
Never mind a 1Ds, if you've got a half decent lens and can execute a stitching routine competently then a stitched Digital Rebel shot would be better! The fact that a compiled image can trounce any single shot capture is digital's dirty little secret. If you want the proof go to Google Earthscape, and zoom in from outer space to see your car parked outside your house.
I shoot mainly architecure/cityscapes with a MF digital back on the same Linhof uber kamera that Michael's currently using. Because buildings don't move around too much they're ideal candidates for stitching. If you've the patience and skill and can afford to invest five or six hours in each image then a stitched shot from a camera costing a fiftieth of my set up would certainly yield superior results. Stitching is the democratisaton of photography, I love it!
But back to your original question. Big sensors tend to deliver better quality because the image chain is less stressed. For any given size of print you're enlarging less, and it's enlargement that allows us to peer at an image's deficiencies. In theory there commensurate and compensating quality gains to be had at every stage of the minaturisation process. In real life these quality gains are more elusive, and you find a sweet spot advantage as you go from APS-C to full frame, and again from full frame to 37x49mm sensors.