Hi. I'm also a 5n user and have only handled Canon's in-store.
Depends upon the shooting but I am approaching video as a compilation of many short shots. Hence, lot's of shorter segments of recording and I have never experienced overheating problems with the 5n. That could be different for you depending...
Very little moire and aliasing but cannot directly compare to Canon.
Cheaper, yes, and I purchased a pricy cold-shoe mount from j-tech and that has been super helpful on many occasions.
Lack of mic input is a pain. That said, I am getting better audio with a shotgun into an external recorder than I would an external mic into the camera. Syncing is an other step.
Form-factor: I found the 550/600D too small for me also in the form factor (I like the 60D) and ed_lee is right, when I'm shooting video, I almost always have some form of stabilization going on, trying to get my hands off the camera itself. Very susceptible to shake without stabilized lenses.
That said, I have three FD lenses and the Sony 16mm and I'm thrilled with what I can produce.
I at times miss the viewfinder when I want to compose a static shot, but for video I would minimally have the LCD Viewfinder for either camera. I have it for the 5n - more stability.
60p conformed to 24p is awesome!
Magic Lantern looks awesome! I am truly envious of that or something similar, but there is no assurance that they didn't "7D" the upcoming 650D and make it harder/impossible to hack. No one knows yet.
No lens that you put on a 650D you cannot put on a Nex, especially with this new Metabones adapter, plus you can put a million lenses on the 5n you cannot on the Canon, including Canon FD lenses. I am also curious about the Sony 50/1.8 because it would be helpful to have something not so sensitive to handling movement.
I am not even pushing for the 5n here. Just a lot more experience with it. It has not limited me for my style of shooting yet.