Like most people here never enough typing patience to add everything. And not mis-information just not all the information. Obviously a CF-B card will be faster when used in a CF-B reader because the reader, having hardware designed to read the card can make the most of its performance. If you have 2000+ images you might see a bit faster download speed but an XQD won't be that far behind the CF-B. A number of issues here to but if you want to find them use google. But with 2000+/a day images you are in a small minority and the difference isn't enough to decide to scrap your XQD for CF-B unless you have an acute bout of GAS or too much money, or are a recent owner of a D850 in which case you would be silly not to go with CF-B. Latest (and more expensive) iterations of CF-B can have very fast speeds, just not in a D850. My wife sometimes can have up to 5000 images so she starts a copy and goes makes tea. In fact in 20 years she has never once complained about downloading taking too long (well not entirely true but more to do with the laptop speed not the actual transfer speed). In fact the longest operation has nothing at all to do with D850s, CF-B or XQD but the length of time to make a backup copy. Leaving aside the time it takes to review and delete the crap.

In a D850 it will only matter if you are doing this commercially, for money, and time is of the essence. If none of these are important (ie for the other 99.99% D850 owners) moving to a CF-B has no speed advantages what-so-ever. Not a rant I was just defending my "mis-information".
In fact you potentially have just created a lot of mis-information. Without the qualifications you noted of of being one of the 0.01% who find a small part of a CF-Bs speed useful you may have left a lot of users expecting to get a performance benefit that just isn't so.

Hmmm. My understanding is that a XQD and the CF-B card work at the same speed in a D850. It is hardware limited. So no you wouldn't necessarily pick the CF-B because its faster in a D850. The CF-B cards might be faster in hardware designed for it but you gain nothing in a D850. So no need to go out and purchase CF-B cards because you think you will gain a speed benefit over your existing XQD cards. Or if you want to buy cards which can be used in possible future purchases. A bit of mis-information here.