I now confess to confusion. I did a lot of reading last night, and found that write (not read) speeds seem to be like smoke. Most manufacturers don't quote them. Some are hazy like "read and write speeds up to".
Then I ran across this article at B&H that refers to the newer Lexar cards. Notice the table in the bottom, which lists a 20MB/s write speed for this fastest of cards.
So I ran off to the Lexar site and all I found there was
"(150MB/s) minimum guaranteed sustained read transfer speed" followed by a footnote "write speeds lower".
So off to Sandisk, where finally (on the Extreme Pro):
100MB/sec* write speed
But that has a fascinating footnote:
* Up to 100MB/sec write speed, read speed lower
OK, never heard of flash memory that wrote faster than it reads. Typo? So I look up at the top of that page in a video they have, and there it says:
Minimum sustained write speed of 20 MB/Sec
Now that's a big difference. OK, I get it, burst vs. sustained, but any card can stick a bit of fast buffer on the front and get a few microseconds of high speed write. But notice that's the same 20MB/s in the Lexar writeup from B&H.