Over at Beyond3d technical forums, resident video game investigator Quaz51 (who also happens to be Eurogamer’s source in their console face-offs), has now proved his suspicions right. MGO renders natively at 1024by768.
This resolution is not 768p as you might suspect, since 1024by768 is not a 16/9 isomorphic resolution. Instead, it’s equivalent resolution (contains the same number of pixels) is 1182by665 - or 665p. It is thus accurate to say MGO renders natively at 665p