Discussion on Reddit on how to make Emacs a bit faster (though nowhere near mg): https://www.reddit.com/r/emacs/comments/3vp583/macros_in_gnu_emacs_and_mg_speed_comparison/
One thing to point out is that the video has several emacs extensions installed, but no mg extensions. I would be interested in seeing how stock emacs (emacs -q) compared.
EDIT: In the reddit thread, someone timed emacs -Q using C-e , C-f and it came it at 1m29s, which is still much slower. According to the others in that thread, it seems to be a dispay engine issue.
C-e , C-f
Agreed - in the mg portion, you can see that it moves to the end of the line only on the one that the point is at, which looks pretty silly, but would definitely make for much faster redisplay.
FWIW I did this test in Emacs on OS X and although it was by no means instant, it took only a handful of seconds or so. (I used C-e , C-f to define the macro.)