Did anybody test these two card types and their effects on buffer size in a D500 or Z6?
When the firmware updates came out to support CFexpress, many people did post their experiences on various forums and websites.
The general picture is that in Nikon cameras which the CFexpress support was added by firmware update, writing to CFexpress cards can be slightly slower than XQD cards. In those Nikons which had CFexpress support from FW 1.0 (Z6II, Z7II, D6), CFexpress is somewhat faster and gives better burst performance, although this difference is nowhere near the difference in the specified speeds for the cards. I guess it may take many generations of cameras before the maximum speeds are actually realized in practice. The same is true of card readers and computers.
Currently sharing one Sony G 440MB/s XQD card between the two cameras and with the borders slowly opening up its time to make the camera kit fully operational again
There is no acute need to switch to CFexpress. If you need to buy new cards, factor in the cost of the reader(s) into the purchase price if buying CFexpress. Or you could buy another XQD card and use the readers that you have, saving a bit of money.