Thanks for the comment and feedback.
Funny you should mention focus, as I'm not entirely sure I had it spot on. I have a manual focuser on that OTA which is great for visual but lousy for AP and it's really quite hard to get it right. I had been using a Bahtinov mask but misplaced it (had to move stuff around for cleaning and now I can't find it!) so focus that night was achieved by eye using the small LiveView screen.
And, quite possibly, the OTA might have had something to do with it. The LX200 is corrected for coma, but not field curvature, so there can be a focus difference across the FOV. For most subjects, it wouldn't be noticeable, as the target is in the centre, but the moon is so darn big ....
Also, as mentioned, video compression in the 600d is at the low end of the quality spectrum (so I've been reading - allegedly quite lossy - though I don't know what the effect is for nearly-still images).