>>1962109hmm, i think /y/ and /u/ are rather similar in what is posted, but I can't say much about their conversations or personalities as boards (of which I know almost nothing about) and I'd think /c/ and /cm/ would be rather similar in terms of what is posted but...
All of that said, I really don't know much at all about the personalities of /cm/ (limited exposure) or /y/ or /u/ (no exposure) so you could be quite right... and you seem to know a good bit about each.