Yes, but I don't really need a Pi 5 and it costs £60.
As above, cost money! :-)
Quite, the BBB has on-board 4Gb EMMC, my BBB (that the RPi is going to replace) has churned away reliably using its EMMC for many years now.
I have another reason (other than my original reasons at start of thread) for moving to a Pi. The pigpio library will allow me to measure some short[ish] times which I can't do so easily on the BBB.