Earth escape Velocity is around 17500 mph. The lunar escape velocity is around 5300 mph. The CSM motor is specified at 20,500 lb thrust yielding a max delta v of around 6300 mph. The ascent module engines were specced to provide a (lunar) thrust to weigh ratio of just over 2:1. On the basis of those figures then both ascent to the CSM and the achievement of lunar escape velocity by the CSM are, theoretically, perfectly viable. After achieving escape velocity and engine shutdown the CSM would have coasted towards earth, once the earth's gravitational pull became greater than that of the moon then the CSM would have begun to accelerate - if we assume rentry speed around the same as lunar escape velocity (actually I think it would have been much higher) then the 3250 average mph for the return journey would appear quite feasible.
The specifications make the trip apparently feasible - the photographic records make me doubt it ever took place. One other little thought crosses my mind - if ordinary scanner radiation can fog film what effect would cosmic radiation have had on the films in the fairly ordinary little cameras the astronauts were using?
Ken.