I think you are asking the right questions. I also ran into weird quality issues. Some shots are really nice, others are very similar to the issue we know from pixel binning at 50fps and above.
>> Use 0,0,0 for dlog, or perhaps 0, -2, 0 for high contrast scenes to slightly improve latitude in post -- NO SHARPNESS REDUCTION FOR DLOG -- is this official? <<
The difference between o sharpness and -1 can be pretty striking in some shots. You can ad sharpening in post, but many details can't be recuparated, so adding filmic grain is the only solution in those cases.
>> Use D-Cinelike (or ART) for standard or lower contrast scenes to get a better distribution of data on the starved bitrate (more data in the midtones) <<
Haven't tested yet, if the problem occurs less with Cinelike.
>> Make sure to ETTR (expose to the right) to keep as much detail as possible. Be careful not to under-expose the Mavic! Remove ND filters if needed and prioritize too high a shutter speed if you must choose between proper shutter and low exposure values. Under-exposing the Mavic is no-go due to the low-bitrate and small sensor. <<
Well, overexposing is a big problem for Mavic's camera as well. So you have to be on the spot. Some low light can be saved or pushed, especially if you have Neatvideo to remove grain.
>> You may set sharpness at -1 (or perhaps even -2?) for Cinelike/ART profiles, but do NOT do this in dlog, as it will cause watercolour effect (because the log profile removes data from the midtones in order to evenly distribute). But, you could reduce sharpness slightly on another profile that has a more even bit distribution <<
From my experience so far my Mavic's picture is almost unusable if you have a lot of small details like trees at -2 sharpness.
>> It seems shooting 2.7k @ 45mbps will give more data per pixel than 4k @ 60mbps? <<
Has anyone tried that out in a bit more scientific manner? So far, I can't see a lot of difference between the 2.7k and the 4k
>> * Does adding Polar Pro filters reduce sharpness at all? Or no affect? <<
Good question. Shoudl try that out. One thing though: If (sun)light falls on your filter (I mean from the side) you loose contrast (that's why we (should) have sunhoods on our lenses). This mostly leads to unusable footage.