I'm not a video guy but I pulled some information from the CFe datasheets.As I understand it, it’s write speed related, only the larger Sandisk cards do more than 1200MB/s, which I think is the cutoff Canon uses.
The Prograde data sheet in the link has a handy table for 4k raw rates (bit depth and fps). It is strange that the table shows that all the Gold cards cannot handle 478MB/s (raw 4K/30fps @12 bit) although the 512GB-1T do handle 500MB/s avg
What would the raw 8K/30 10 bit data speed be and which cards would support it?
Still bursts could be more relevant for max write speeds but why aren't the card manufacturers listing avg write speed which video will be and avg read speed?
progradedigital dot com/products/cfexpress/
600MG/s Gold 120GB => Avg 145MB/s
1000MB/s Gold 256GB => 350MB/s
1000MB/s Gold 512GB-1T => 500MB/s
1400MB/s Cobalt 325GB => 1300MB/s
The avg to max speed difference is huge from 25% to 50% for gold but cobalt is pretty close to max.
Sandisk write speeds with no mention of sustained/average speed! link is:
shop dot westerndigital dot com/products/memory-cards/sandisk-extreme-pro-cfexpress-type-b#SDCFE-064G-ANCIN
64GB 800 MB/s
128/256GB 1200 MB/s
521GB 1400 MB/s
Lexar. I can't find a datasheet for them... only 64GB — 512GB Up to 1750MB/s read, up to 1000MB/s write.
If Lexar 128/256GB cards are okay for the 1DXiii (assumed) 1000MB/s then why aren't the Sandisk 128/256GB included?