Why not 10? 1 byte ~= 1k values. Nice easy conversions.

Weird bytelengths were very much the norm in early computing but noone (seemingly) ever mass-produced a 10 bit computer[1].

   In the first 3⁄4 of the 20th century, n is often 12, 18, 24, 30, 36, 48 or 60. In the last 1⁄3 of the 20th century, n is often 8, 16, or 32, and in the 21st century, n is often 16, 32 or 64, but other sizes have been used (including 6, 39, 128).

I used to use a 32 bit bite! Then I has my wisdom teeth removed, and now I have a 28 bit bite.