Hi Jack, I've one of the fastest SanDisk 64GB Extreme Pro SD Speicherkarte 300MB/s UHS-II.
I really can recommed this card for focus stacking.
My Canon R5 uses CFE cards and I use the 256GB ones which allows me about 1500 images which is usually good for a morning’s shoot. Standard SD cards are too slow to keep up with 20fps bursts.