Theoretically, >600kbps UART will be enough. The openlog blackbox firmware supports up to 1Mbps:https://github.com/cleanflight/blackbox-firmware/blob/master/OpenLog_v3_Blackbox/OpenLog_v3_Blackbox.ino#L87 It doesn't, max reliable baud rate is 115200. 578056.1122244489bps...