Thanks to @TomTheDP for finding this comparison between the Original BMPCC and Alexa, and thanks to Alain Bourassa for performing the test! As @Matt Kieley says, the BMPCC and BMMCC have the same sensor, so it's a proxy for the BMMCC as well.
Not a bad match, considering that this appears to have no adjustments, and shots have different White Balances:
The WB comparison:
Latitude tests:
What I see from this comparison is:
Obviously the Alexa has more latitude, no surprises there
Both comparisons vary quite a bit in tone and levels between the shots
(this is an indication to me that the shots were taken quickly and the results not processed too much, so I think is a good indicator of what things are like when used for real rather than in meticulous lab environments)
The BMPCC fails at +4 and the Alexa doesn't, but both look reasonable at -3, so the highlights are where the Alexas increased DR is revealed
The BMPCC looks very usable across the whole range and this reflects my impressions of shooting with it
Vectorscope comparisons, with colours extended 2X in the scope for ease of viewing..
BMPCC Primaries:
Alexa Primaries:
BMPCC chart:
Alexa chart:
For reference, this is a colour chart I shot with my GH5. The absolute level of saturation can't be compared as I can't remember what I did in post, but check out how different the overall shape is, which is much closer to 'correct':
I suggest this is a very good result, especially considering how old and how cheap this camera is, even after the price has risen since COVID lockdown and nostalgia shopping.