Thanks for the link!It appears to me (I'm the guy who did those tests for all the CFe brands on the R5) that the buffer is about the same in terms of gross memory between the A1 and the R5. We'll see when we get an A1 in hand to test. But the CFe A card is going to have 1/2 the performance of the CFe B cards, so the buffer will clear in 2x the time it takes to clear the buffer on the R5.
That said, the best cards clear the R5 buffer in 4-6 seconds, so doubling that is not too terrible. The data you cite below in The Digital Picture table must have used one of the slower cards. The better data we have indicates that the A1, after shooting for about 5 seconds, will need to clear buffer for about 8-12 seconds, depending on how fast your card is. It should be noted that the ONLY card manufacturer making CFe A cards is Sony. I've tested them in an A7s III, and they're pretty good (if expensive and not terribly large). Sony's CFe B cards are among the fastest in that category.
Most realistically, people aren't going to be shooting in 30 fps. They're more likely to be shooting at lower rates because, well, sanity. As a result, they'll likely take more like 8 seconds to fill a buffer and another 8 to clear it. If you burst on and off, you might manage to not hit the end of the buffer, but you're likely to hit it much more often than you do in the R5. The R5, by the way, is fantastic in this regard. I'm a long-time perpetrator of spray-and-pray with wildlife shooting, and I come against the buffer so infrequently, that I've done entire shoots mistakenly writing to my SD card and never noticed because the large cache was protecting me from hitting the wall.
Updated data on R5 CFexpress performance across brands here. They'll be adding the CFe Type A data shortly, as well as data on Nikon and Panasonic CFe Type B performance (which wasn't great).
I might have missed it but all the tests appear to be using the CFe card only ie not when writing to both SD and CFe cards at the same time. Is that correct? It would be good to understand if there are limitations especially for the buffer clearing rates when using a SD card as well. I have a Sandisk 128GB USH-II SD card which was one of the top 10 in write speeds @ ~200MB/s but this pales into insignificance compared to the CFe B card.