For the eMMC, quite probably.

The BBB Rev B BOM lists a Micron chip that tops out at 30MB/s read and 6.6MB/s write (pretty close to measured).

The BBB Rev C BOM lists Micron chips in that range but also lists chips like the Kingston EMMC04G-M627 which is capable of 250MB/s read and 25 MB/s write.

This link seems to indicate that the Rev C is around 2x faster on eMMC. https://www.tablix.org/~avian/blog/archives/2017/08/beagleco...

(the RPi Zero numbers seem to correlate with yours so it seems you are measuring the same things)

So, the eMMC numbers are going to be highly specific to the board manufactured.