BeagleBone Black and Green microSD and onboard flash performance

Looks like I get about 4.3MB/sec when writing to the onboard flash on my BeagleBone Black, and about 7.1MB/sec when writing to a 64GB Sandisk Ultra 64GB microSD card.

On BeagleBone Green, I get 9.4MB/s to onboard flash, and 6.8MB/s to the same SanDisk microSD card.

I used this command to test:
$ time ( dd of=foo if=/dev/zero bs=1M count=100 ; sync )

Ignored dd's report, and divided 100 / elapsed time as reported by the time command.