Welp, I did some testing on rolling shutter with and without the bitrate monster.
Lens: 18-135 IS. (non-STM version)
Focal length: 135mm
First up: The default firmware:http://i.imgur.com/nS3aa.jpg
Here's with the bitrate monster at CBR 20.0x and flush at 3, which I believe is the maximum that the ML can pull out of the camera:http://i.imgur.com/mrbcI.jpg
Here's the two, overlaid on top of each other:http://i.imgur.com/Zkrqr.jpg
There's a slight increase of rolling shutter in the bitrate monster's but I'd chalk that one up as:
a. Margin of Error due to that I had to do this by hand one setting after another, and not at the same time.
b. Very slight sample variance.
That I'd say there's practically no difference in rolling shutter.
Another thing that I can conclude from the test is that if you look at the grain pattern on the wood part, and the nail details, you can definitely see definition in the All-I version while it's all washed out in the default firmware version. Thus concluding that ALL-I have a definite net positive benefit in image resolution. Keep in mind that this is ISO 12,800.In summation:
a. Rolling shutter difference is negligible or insignificant
b. ALL-I has a demonstrable benefit in resolution
One thing I can't seem to explain is that the highlight seems to be blown out in the default firmware version, while it's more retained in the bitmonster. I'm not sure if something changes in the setting while I load ML (doubt it) or if high bitrate ALL-I somehow lets it retain more highlight detail.
UPDATE: I did some more quick test, and I'm seeing it: The bitmonster seems to be retaining highlight details much better at ISO 12800.
UPDATE2: false alarm on the highlight thing. Apparently, under certain circumstances, after you record some movies with default firmware, then load up ML, and go to movie-live-view mode with ML, it would stop down the aperture by one stop. Not sure what triggers it, it happens rather randomly.