I'm not sure why they are going with UHS-II. That's 312 MB/sec (bus speed, not write speed). The files are about 25 MB each. 25 MB * 20 fps = 500 MB/sec. How big of a buffer do you get and how long will it take to clear? Now, at the 12 fps rate, it's not so bad (300 MB/sec).
CFExpress is 1600 MB/sec.
It's the same with the
Sony a9:
Continuous Hi
Compressed RAW
0.05 second
(20.00 fps);
240 frames total;
45 seconds to clear*
Time per shot, averaged over 240 frames, then slowed to an average of about 0.29s or 3.40 fps when buffer was full with a lot of variation.