so far the reasoning I'm getting for the 8-bit byte seems to be:
1. you want your byte size to be a power of 2. This is EXTREMELY believable to me, but I don't understand why exactly you want this, my understanding of CPU design is very bad. Maybe it's because of busses? (what's a bus?)
2. 4 bits is too small, you can't fit a character into 4 bits
3. you also don't want your bytes to be too big, and 8 bits was working well, so the byte size never got bigger after the move from 4 to 8