I just changed my CFe for my R5 from Sony 1450 mb/s to Lexar 1700 mb/s.
This improved the buffer size from 38 to 42 RAW pictures. How big would it be if 3300mb/s would be possible?
The funny thing is that the R5 tops out at writing 400-450MByte/s, so the improvement you are seeing isn't from the 1450 to 1700 top write speed jump, but more likely from the (some handwaving ahead) 350 to 400
sustained write speed jump. The newer CFe cards tend to have the VPG400 certification, which guarantees a sustained write speed of at least 400MByte/s.
AFAIK the only CFe cameras that can use the full CFe bandwidth are the Nikon Z9 and Z8. And Nikon cameras allow you to keep shooting after the buffer has filled, at a rate that matches the card speed. Canon bodies will pause a long time to clear a large chunk of the buffer, take a bust of pictures, pause again, etc. So Nikon will give you a consistent framerate after the buffer has filled, Canon does the hurry-up-and-wait thing
So there's 3 things Canon will hopefully do in the R5II/R1:
- Support CFe 4.0
- Make the Digic fast enough to support the 3300MByte/s top speed of CFe 4.0 cards
- Change the buffer overflow algorithm to be more like Nikon