I believe the 100Mbs is only in 4K mode.
The
MM1 can only go as high as 2.7K so it doesn't need as fast a bit rate to maintain the same minimum compression as 4K on the
MM2.
One would need to compare bit rate at the same 2.7K on both models to see if there really is an improvement in minimum compression.
2.7k isn't that much smaller than 4K (compared to 1080p).
Also 100Mbps is usually set as the maximum but doesn't always record at the maximum (usually 'overall' it can be between 50 to 80 depending on scene details).
All recording sizes are 'variable' bit rate, 4:2:0, 8-bit YUV
Tested with a scene of high level of detail with adequate lighting. Data from "MediaInfo" shown in Media Player Plus.
4K 24p
Variable Bit rate mode
94Mbps overall
100Mb/s "Maximum Bitrate"
2.7K 24p
Variable Bit Rate Mode
40.0Mb/s Overall
40.0Mb/s Bit rate (no 'maximum' designation)
1080p 24p
Variable Bit Rate Mode
32.1Mb/s Overall
35.0Mb/s Bit rate (no 'maximum' designation)
So I guess it would seem that for 2.7K it's capped for 40Mb/s, and 1080p capped for 35Mb/s, with 4K being the only one that's capped for 100Mb/s, in which case 4K for intention of scaling down to 2.7K would still yield more information than 2.7K @ 40Mb/s (like I said, 2.7k is only about 0.71x of 4K).
On my old Panasonic GH1, which had an original maximum bit rate of 17Mb/s , after the firmware was finally hacked it was able to be set to 100Mb/s (not without some buffer issues depending on configuration to where 75 was more realistic), it was possible to manually adjust each recording mode to a specific maximum bit rate, but the main time that was useful was hacking the Motion-Jpeg 720p mode into becoming 1536x960 (somewhere in between 720p and 1080p) setting it to 4:2:2 color, and using the increased bit rate for much better color retention purposes such as chroma keying off a green screen.
So would like to see more bit rate in 2.7K as it would still be useful, but would be far more useful if it could somehow be processed as 4:2:2 instead of 4:2:0.
Edit: in case it wasn't already known, but if you have 4K footage at 4:2:0 8-bit, and transcode it to DNxHD or ProRes 1080p (you cannot crop or edit at all in transcoding, just a straight transcode), you will end up with 1080p 4:4:4 , but not quite 10-bit (somewhere closer to 9-bit color) color wise, a good improvement to shooting in 1080p 4:2:0. Only really useful if you're a professional or colorist really trying to squeeze out fidelity/tone, especially since it takes additional time and computing to transcode.