Because of the big impact the card type and speed has on the Z9 buffer, I tried with the z6 out of curiosity. I only had two cards at hand today, same 64gb capacity, both sony xqd G, read 440mb/s write 400mb/s. Exact same card.
On h*, raw 14 bit the results were
Z61, card1: 55 shots
Z62, card2: 35 shots
Kind of weird...I switched cards and the results were
Z61, card2: 34 shots
Z62, card1: 55 shots
I was worried about a lesser camera but the difference is the card performance. They both come from kits, already in the camera box so I mostly reject the possibility of a fake card.
I have heard of sample variation on lenses but not on memory cards, and not by this huge margin.