Sandisk has released an A2 application class micro sd card that at least on paper will be the undisputed performance king for the Pi. Only trouble is, it costs as much as 10 Pi 3's and is way overkill for the majority of people.
Specs are very impressive:
400GB, A2 application class (4000/2000 minimum IOPs r/w)
160 MB/s read
90 MB/s write
https://www.sandisk.com/home/memory-car ... rosd-400gb
Hopefully that speed class will trickle down to card price classes more suitable for usage with the Pi.